referring first to fig1 and 4 , there is shown an optimized data entry keyboard 110 which , according to the present invention , is completely operational by a single human hand and includes all standard alphabetic , numeric , punctuation and function keys found on a standard two hand electronic data entry keyboard . the right - hand keyboard 110 includes a keyboard housing 112 , and four rows of keys 114 , 116 , 118 and 120 , with four of the keys 122 , 123 , 124 and 125 serving as the home keys in row 114 . in that regard , key 122 is the home key for the right index finger ; key 123 is the home key for the right middle finger ; key 124 is the home key for the right ring finger ; and key 125 is the home key for the right little finger . as shown in fig4 the &# 34 ; shift &# 34 ; key 136 is easily operated by the right thumb . keys 132 - 142 serve various conventional keyboard features which are indicated by legends on those keys ( except key 137 , which contains no legend and functions as a conventional &# 34 ; space bar &# 34 ;). the right - hand keyboard 110 also includes special function keys 144 , 146 , 148 and 150 , the purpose for which will be explained in greater detail below . it is thus seen that in the optimum right - hand keyboard 110 , the home keys are formed respectively by the letters t - e - a - o . fig3 is a finger stroke reference diagram , showing paths depicted by arrows indicating which fingers on the right hand are used to stroke each key , and with the encircled numerals 1 through 26 indicating arbitrary reference numbers used to identify key selection in column 1 of table 1 . in accordance with the present invention , it will be understood that the fingers on the right hand can depress all of the alphanumeric keys in rows 114 , 116 , 118 and 120 by moving less than three key positions from the center , home row 114 , as depicted by the arrows in fig3 . there is also shown in fig2 and 5 , an optimized left - hand keyboard 210 mounted in a keyboard housing 212 , and defining four rows 214 , 216 , 218 and 220 in a manner similar to the right - hand keyboard 110 of fig1 . home keys for the left - hand keyboard 210 are defined by keys 222 - 225 . in this regard , key 222 functions as the home key for the left index finger ; key 223 serves as the home key for the left middle finger ; key 224 serves as the home key for the left ring finger ; and key 225 serves as the home key for the left little finger . likewise , the &# 34 ; shift &# 34 ; key 236 if easily operated by the left thumb , as indicated by fig5 . in a manner similar to that shown with respect to the right - hand keyboard depicted in fig3 the left - hand keyboard of fig2 and 5 likewise permits the fingers on the left hand to depress all of the alphanumeric keys in rows 214 , 216 , 218 and 220 by moving less than three key positions from the home keys 225 in the center home row 214 . it will be further understood by comparing fig1 and 4 with fig2 and 5 that the left - hand keyboard 210 of fig2 is essentially a &# 34 ; mirror image &# 34 ; of the right - hand keyboard 110 shown in fig1 such that the same finger on the right hand depresses the same keys as the same finger on the left hand , with the same relative work effort being exerted by the same finger for the same key . it will further be appreciated by those skilled in the art that all keys remain within the normal span for a right or left hand as that of a standard , two - handed keyboard , which typically is about five inches from the little finger to the index finger . the manner in which the optimal position for each key on the keyboards 110 and 210 is selected will now be described with reference to fig3 and table 1 set out below . table 1 is used to determine the distance that the four fingers of either hand must travel from their assigned &# 34 ; home &# 34 ; position when selecting any other key , and is useful in assigning an ordered number sequence to the alphabetic keys based on the amount of work required for each finger to select a desired key . table 1__________________________________________________________________________minimum work effort key sequenceoptimization calculation table relative relative minimum - path lateral vertical finger work to work keyref distance distance effort select key sequence ( 1 ) ( 2 ) ( 3 ) ( 4 ) ( 5 ) ( 6 ) __________________________________________________________________________1 - 1 0 . 000 0 . 100 1 . 00 0 . 100 11 - 5 0 . 839 0 . 100 1 . 00 0 . 939 81 - 6 0 . 839 0 . 100 1 . 00 0 . 939 71 - 7 1 . 352 0 . 100 1 . 00 1 . 452 121 - 8 0 . 750 0 . 100 1 . 00 0 . 850 51 - 9 1 . 500 0 . 100 1 . 00 1 . 600 131 - 10 1 . 250 0 . 100 1 . 00 1 . 350 111 - 11 0 . 791 0 . 100 1 . 00 0 . 891 61 - 12 2 . 035 0 . 100 1 . 00 2 . 135 221 - 13 1 . 625 0 . 100 1 . 00 1 . 725 161 - 14 1 . 505 0 . 100 1 . 00 1 . 605 142 - 2 0 . 000 0 . 100 1 . 33 0 . 133 22 - 15 0 . 839 0 . 100 1 . 33 1 . 249 102 - 16 0 . 791 0 . 100 1 . 33 1 . 185 92 - 17 1 . 505 0 . 100 1 . 33 2 . 135 233 - 3 0 . 000 0 . 100 2 . 00 0 . 200 33 - 18 0 . 839 0 . 100 2 . 00 1 . 878 193 - 19 0 . 791 0 . 100 2 . 00 1 . 782 173 - 20 1 . 505 0 . 100 2 . 00 3 . 210 244 - 4 0 . 000 0 . 100 2 . 00 0 . 200 44 - 21 0 . 839 0 . 100 2 . 00 1 . 878 204 - 22 0 . 750 0 . 100 2 . 00 1 . 700 154 - 23 0 . 791 0 . 100 2 . 00 1 . 782 184 - 24 0 . 901 0 . 100 2 . 00 2 . 002 214 - 25 1 . 505 0 . 100 2 . 00 3 . 210 254 - 26 0 . 737 0 . 100 2 . 00 3 . 674 26total relative work - all keys ( 7 ): 39 . 804__________________________________________________________________________ in table 1 , column 1 is designated &# 34 ; path ref &# 34 ; and refers to the finger stroke paths depicted in fig3 for finger movements relative to the home keys 122 - 125 for keyboard 110 and keys 222 - 225 for keyboard 210 ( see fig3 ). column 2 of table 1 refers to the &# 34 ; lateral distance &# 34 ; and indicates the distance travelled horizontally between each &# 34 ; home &# 34 ; key 122 - 125 or 222 - 225 and another selected key for each finger movement . column 3 of table 1 is the &# 34 ; vertical distance &# 34 ;, and indicates the vertical movement component of the key when depressed . column 4 of table 1 indicates the &# 34 ; relative strength &# 34 ;, indicating the results of tests which were conducted to obtain the relative strength on each of the four fingers needed to depress a key . those measured results for typical individuals are : continuing , column 5 of table 1 indicates the &# 34 ; relative work to select key &# 34 ; and is the product of the relative finger effort of column 4 times the sum of the vertical and lateral distances tabulated in columns 2 and 3 , respectively . column 6 indicates the &# 34 ; minimum work key sequence &# 34 ; as an ordered arrangement of each key in terms of the relative work to select each key . the higher the sequence number , the higher the work effort required to select that key . finally , the bottom entry as number 7 in table 1 indicates the &# 34 ; total relative work &# 34 ; which is the sum of the work effort for all of the keys , and indicates a measure of keyboard work efficiency which can be used to select optimum home key locations and key - to - finger assignments . by way of example , shifting the four finger home keys one key to the left results in a total relative work of 40 . 108 , which is higher than the total relative work of 39 . 804 given in table 1 . it will therefore be understood that , using the analysis set out in fig3 and table 1 , the optimum numbering sequence for the right - hand keyboard is shown in fig4 and the left - hand keyboard in fig5 . the data in column 6 of table 1 is then used to assign alphabet letters to keys based on the frequency of occurrence of each letter in the english language . referring now to table 2 set out on page 16 , there is shown the relative frequency of occurrence for letters in the english language . using this data , the letters of the alphabet are arranged on the keys by assigning the highest frequency letters to the lowest work effort keys as determined in table 1 . thus , the letter &# 34 ; e &# 34 ; is assigned to key 123 , the letter &# 34 ; t &# 34 ; is assigned to key 122 , the letter &# 34 ; a &# 34 ; is assigned to key 124 and the letter &# 34 ; o &# 34 ; is assigned to key 125 . this arrangement continues in descending order of frequency , with the key for the letter &# 34 ; z &# 34 ; appearing in the location indicated by the encircled numeral 26 in fig3 . of course , there remains the task of assigning numerals and grammatic symbols to the keys as well . as indicated for the right - hand keyboard 110 in fig6 and the left - hand keyboard 210 in fig7 arabic numerals are assigned to keys by the indicated number with the prefix &# 34 ; n &# 34 ;. the 32 grammatic symbols are assigned to keys utilizing table 3 . table 2______________________________________relative frequency of lettersin the english alphabet descending order ofletter frequency______________________________________e 1t 2a 3o 4n 5r 6i 7s 8h 9d 10l 11f 12c 13m 14u 15g 16y 17p 18w 19b 20v 21k 22x 23j 24q 25z 26______________________________________ table 3______________________________________relative frequency of symbols . sup . 1 descending descending order of order ofsymbol frequency symbol frequency______________________________________ ` 1 * 17 · 2 & amp ; 18 ; 3 = 19 : 4 @ 20 ? 5 + 21 6 [ 22 / 7 ] 23 &# 34 ; 8 & lt ; 24 &# 39 ; 9 & gt ; 25 ( 10 { 26 ) 11 } 27 $ 12 28 - 13 ˜ 29 ! 14 ## str1 ## 30 % 15 ## str2 ## 31 # 16 ` 32______________________________________ . sup . 1 frequency order based on inventor &# 39 ; s survey and on layout of typica keyboards for personal computers .? referring again to fig6 and 7 with reference to table 3 , it is seen that the various entries of table 3 are reflected by encircled reference numerals indicated in each of fig6 and 7 . by way of example , the &# 34 ;,&# 34 ; symbol has the highest order of frequency , and is therefore assigned to key 123 ; the &# 34 ;.&# 34 ; symbol has the second highest order of frequency , and is assigned to key 124 ; the &# 34 ;;&# 34 ; symbol has the third highest order of frequency , and is assigned to key 125 ; and so forth , as reflected in table 3 and depicted in fig6 and 7 . the keyboards 110 and 210 resulting from the analysis of fig3 and 6 ( right - hand keyboard ) and fig7 ( left - hand keyboard ) together with tables 1 , 2 and 3 are depicted in fig8 and 9 , respectively , and represent one optimal arrangement for the alphabetic , numeric and symbol keys for a one - hand keyboard . however , there are other features associated with the keyboards 110 and 210 which may justify a further optimization of the keyboard arrangement , and which will be discussed in greater detail below . referring again to fig1 and 2 , two special keys labelled keyswitch and shft - keyswitch , respectively , are provided for each of the keyboards 110 and 210 . for the right - hand keyboard 110 of fig1 the keyswitch is designated by reference numeral 148 , and the shft - keyswitch is designated by reference numeral 150 ; the similar keys on the left - hand keyboard 210 of fig2 are designated by reference numerals 248 and 250 , respectively . these keys are provided to enable the use of a single key to generate numeric or symbol characters in addition to the alphabetic characters assigned to a selected key . this multi - use capability is accomplished in the present invention by the addition of these keys 148 , 150 and 248 , 250 in a manner similar to the standard shift key of a conventional qwerty keyboard , but are in addition to the standard shift key and are located in a position easily accessible by the thumb of each corresponding hand . by using the thumb to depress these keys in conjunction with other keys , multiple - character use of a selected key can be obtained . in addition to the multi - character key functions of keys 148 , 150 and 248 , 250 described in section 2 above , the one - handed keyboards of the present invention are provided with additional enhancements to further facilitate efficient one - handed operation . these features are added to accommodate the simultaneous character input combinations required by some computer word processing and applications software . referring now to fig1 and 2 , the present invention contemplates three types of key combination inputs : a ) dual - function ( e . g ., shft - tab ) key 134 and dual prefix ( e . g ., ctrl - shft , shft - alt ) keys 142 , 138 within the main shell 112 which generate the indicated two - key sequence with a single keystroke . b ) special single character hold - down key 144 ( labeled single key hold / auto rel in fig1 )-- depressing this key , followed by any other two - key sequence , results in the simultaneous transmittal of the selected two - key combination at the moment the second character key is depressed . c ) special multiple character hold - down key ( labeled multi key hold / man rel in fig1 ) with manual release of any selected multiple - key combination when this special hold - down key is depressed a second time . thus , in accordance with the present invention , keys 144 and 146 facilitate the efficient one - hand operation of the keyboard 110 ( and likewise keyboard 210 of fig2 ) by accommodating multiple - character input combinations as required by some computer application software . the single character hold down key 144 provides automatic release of any selected two - key combination when the second of the two - key combination keys is depressed . the single - key 146 provides manual release of any selected multi - key combination when this special hold down key is depressed a second time . referring now to fig1 , it is clear that these special function keys 144 , 146 , 148 and 150 of keyboard 110 ( and the corresponding keys for left - handed keyboard 210 ) are particularly useful when the basic one - hand keyboard 110 or 210 is included as the alphanumeric portion of a typical &# 34 ; 101 key &# 34 ; keyboard , as is used with computers today . for example , it would heretofore be extremely awkward or impossible to generate the sequence &# 34 ; ctrl - shft - f12 &# 34 ; with one hand on a standard keyboard , because of the physical separation of those keys . in the present invention , this sequence is easily accomplished with the three - stroke sequence &# 34 ; single key hold / auto rel . . . ctrl - shft . . . f12 &# 34 ; ( the left - hand keyboard is similarly depicted in fig1 ). referring now to fig1 , there is shown one example of a flow chart executed by logic circuitry within the keyboard to provide the single - key hold / manual release function of key 146 . in algorithm module step 160 , the keyboard senses whether or not the single - key hold / manual release key 146 ( or the corresponding key 246 ) has been depressed . if depressed , the keyboard disables the register output as shown by step 16b , and waits for another key to be depressed , as represented by step 162 . as an output from step 164 , the keyboard 110 stores the character corresponding to the alphabet key that was depressed as step 162 , and the keyboard waits for a second alphabet character key to be depressed , as represented by step 168 , after which that character is also added to the register storage as indicated by step 170 . simultaneously , the step 170 enables the register output as indicated by step 172 , enabling an output from the storage register 174 as a two character output combination , represented by step 176 . fig1 is a flow chart depicting the electronic sequence for use with multi - key 146 for keyboard 110 , and multi - key 246 for keyboard 210 . prior to depressing the multi - key 146 , counter n is at its normal &# 34 ; 0 &# 34 ; state . the sequence is initiated by depression of one of the multi - keys , as indicated by step 180 and counter n is simultaneously incremented by 1 . if counter is less than or equal to 1 , then the register output is disabled as the keyboard waits for the next series of character keys to be depressed . thereafter , each character depressed is indicated by an output to the storage register 186 , including outputs 190 , 191 and 192 . following depression of the last desired character keys , the multi - key 146 is depressed a second time and counter n is incremented by 1 . decision module 182 now detects that counter n is greater than 1 and subsequently the output register is enabled and the counter n is reset to &# 34 ; 0 &# 34 ; as indicated in step 184 . this permits an output from storage register 186 as indicated by the combination output 194 . a final preferred arrangement of the keys for keyboard 110 and 210 will be described with reference to fig1 and 11 , and which additional consideration is given to the arrangement of the keys to minimize the probability of successive finger strikes by the same finger , based on standard lists of common two - letter combinations . additionally , customary paired symbol groups have been located adjacent to each other on the final preferred arrangement of keys shown in fig1 and 11 . in each case , the choice of key location involves the evaluation of finger movement work effort and selections made to minimize total work effort and to minimize consecutive finger strikes by the same finger for the final keyboard arrangement . it will of course be understood by comparison of fig1 and 11 that the same keyboard layout is illustrated in fig1 and 2 . referring now to fig1 , it will be appreciated by those skilled in the art that the right - hand keyboard 110 and the left - hand keyboard 210 may be easily interchanged in a modular manner with a conventional qwerty two - handed keyboard 310 , for insertion with a keyboard shell 300 , and may be adapted for conventional interconnection schemes found in such keyboard shells . another feature of the present invention will now be described with reference to fig1 and 19 , which illustrate a rotatable keyboard system which permits easy selection of a one - hand keyboard for use with either the right or left hand . the keyboard system 410 includes a shell 412 having a central opening defined by inner surfaces 414 , 415 , 416 and 417 , which are disposed in a generally rectangular configuration . a keyboard support 418 is mounted in the opening defined by the surfaces 414 - 417 via a pivot 424 at each side of the keyboard support . the keyboard support 418 has opposing first and second surfaces 426 and 428 . a right - hand keyboard 110 in accordance with the discussion set out above and as illustrated in fig1 is disposed in the first surface 426 , and a left - hand keyboard 210 is disposed in the second surface 428 . as shown in fig1 , the keyboard support 418 is easily rotated through an arc 430 to permit the selection of either a right - hand keyboard 110 or a left - hand keyboard 210 . while a one - hand keyboard ( for either the right or left hand ) has particular utility for disabled persons with only one hand , ready access to either a right - or left - hand keyboard in accordance with the arrangement shown in fig1 and 19 will permit a person having a capacity to use both hands the opportunity to avoid the fatigue and stresses which often lead to permanent injuries , for example the well - known carpal - tunnel syndrome . it will thus be understood from the above description that the one - handed keyboard arrangements provide the following features : a ) individual , manually operable keys , 5 rows of standard keys , character keys having nominal 0 . 75 &# 34 ; center spacing in both horizontal and vertical directions , alternating 6 and 7 keys in juxtaposed rows from the bottom to top . b ) the maximum distance of the center of any alphabetic key from the center of any home key being less than about two inches . c ) twenty - six alphabet keys which also include ten numbers and thirty - two symbols which are utilized in conjunction with the special keyswitch and shft - keyswitch control keys . d ) special single key hold / auto release and multi - key hold / manual release function keys and a process for their use in generating multiple character combinations with one hand . e ) two keyboard layouts which include all functions of the standard &# 34 ; 101 key &# 34 ; keyboards now commonly in use , but which incorporate the left and right one - hand shell , respectively , of the present invention in place of the standard two - hand alphanumeric / symbol shell of the standard &# 34 ; 101 key &# 34 ; keyboard . f ) a modular keyboard layout which allows choice of left - hand , right - hand , or standard shells which are insertable into the otherwise standard &# 34 ; 101 key &# 34 ; keyboard arrangement . g ) the processes described for using the above keyboard layouts to make possible one - hand input of typical documents and data with speed and efficiency equal to that of a two - handed person using a conventional keyboard such as might be found with computer systems today . h ) a rotatable keyboard system permitting easy selection of either a right - hand or left - hand keyboard . this concludes the description of the preferred embodiments . a reading by those skilled in the art will bring to mind various changes without departing from the spirit and scope of the invention . it is intended , however , that the invention only be limited by the following appended claims .