the preferred embodiment of the present invention will be explained hereinunder in detail with reference to the accompanying drawings . fig2 is a block diagram for illustrating the schematic configuration of an electronic apparatus having a one - piece type input and output section in which a coordinate input section is overlapped on a display section . shown in the figure is a transparent input tablet 21 in which a resistance film , a transparent electrode , etc . are used . it accepts coordinate inputs when a tablet surface position is indicated , by pressing , with an indicating pen 23 . the input tablet 21 is formed of a glass plate in which a resistance film is formed by depositing or printing a material such as ito , etc . and a pet film . the resistance film surfaces of the glass plate and the film are overlappingly positioned so as to face each other . further , a spacer ( not shown ), such as a very small silicon rubber , is disposed between them so that when the surface ( coordinate input surface ) of the film is pressed the resistance films of the two are brought into contact with each other at the press point . over all of the glass plate and the film is formed a conductive pattern as a terminal ( electrode ) for applying a voltage to the resistance film and measuring a potential at both ends of the resistance film . shown also in the figure are a press point detection circuit 22 , for applying a predetermined voltage to both ends of a resistance film and measuring its potential , which detects a press point position with the indicating pen 23 on the basis of the magnitude of a measured potential , a dot - matrix type liquid crystal display board 25 which is driven by a liquid crystal driving circuit 24 and which displays numerous kinds of data , icons for use in input , and numerous kinds of messages , and a processing section 20 comprising a cpu 111 , a rom 112 , and a ram 113 , which controls the input / output section and performs input and output processing on numerous kinds of information . in the case of an electronic apparatus of this embodiment , since it does not have an input apparatus other than the input tablet 21 , not only data but instructions of numerous kinds of commands , etc . are all input by using this input tablet 21 . the input tablet 21 is overlappingly positioned on the liquid crystal display board 25 and can be seen through the display of the liquid crystal display board 25 , as shown in fig3 . a seal 31 , on which a symbol for a soft switch is printed , is pasted on a substrate 30 on which the liquid crystal display board 25 and the liquid crystal driving circuit 24 ( not shown in fig3 ) are mounted . the input area of the input tablet 21 has a size which includes the liquid crystal display board 25 and the seal 31 . the soft switch symbols on the seal 31 , in addition to those on the display screen , can be input by pressing the input tablet 21 . next , a case where an indicated point is input by pressing the surface of the input tablet 21 will be explained . as shown in fig4 ( a ), let both ends of resistance films formed on the glass plate and the pet film be a , b , and c , d respectively . the resistance films are not in contact with each other at first , but if pressed by the indicating pen 23 , they are brought into contact with each other at a press point p . to detect the coordinates of this p point on the x axis , as shown in fig4 ( b ), a predetermined voltage is applied between a and b beforehand , and the potential at the point p is measured on the basis of the potential at the c point ( or d point ). on the other hand , to detect the coordinates of this p point on the y axis , as shown in fig4 ( c ), a predetermined voltage is applied between c and d beforehand , and the potential of the point p is measured at the a point ( or b point ). the position of the indicated point p is detected by performing the above action alternately . fig5 is a view for explaining the configuration of a press point detection circuit 22 . shown in the figure is an x / y switching circuit 51 for switching to detect the coordinates of either the x axis or the y axis . each of the terminals a to d of the resistance film shown in fig4 is connected to an operational amplifier 53 via the x / y switching circuit 51 . the operational amplifier 53 is made a voltage follower , so a voltage drop across a and p , or across c and p , can be ignored . shown also in the figure is an a / d converter for converting a voltage output from the operational amplifier 53 into digital data . the output of this a / d converter 52 is read out by the processing section 20 to detect the position of the press point p . since the input terminal of the operational amplifier 53 has been pulled down by a resistor 54 having 1 to 2 mω , a ground potential is measured in the a / d converter 52 when there is no pressing . next , a scheme of a calibration for matching the coordinate systems of the coordinate input section ( input tablet 21 ) and the display section ( liquid crystal display board 25 ) will be described in detail . to make the coordinate systems in agreement , the following steps must be performed . first , 2 d will be explained . unit length ( i . e ., length represented by one bit ) should be set smaller than the display dot pitch of the liquid crystal display board 25 . here , by taking into account the resolution required for character recognition , let it be 0 . 1 mm . since the position data ( hereinafter called an ad value ) which is output from the a / d converter 52 is not necessarily in units of 0 . 1 mm , the unit length must be converted to 0 . 1 mm by multiplying it by a certain correction coefficient . to determine a correction coefficient , for example , four points p 1 to p 4 , as shown in fig6 ( a ) may in turn be indicated by pressing and an ad value is sampled . if the ad value determined by pressing a point p n with the indicating pen 23 is denoted by ( adx n , ady n ), correction coefficient on the x axis is ## equ1 ## correction coefficient on the y axis is ## equ2 ## where p 1 p 2 and p 3 p 4 are numeric values with the distances between p 1 p 2 and p 3 p 4 in the units of 0 . 1 mm . next , 1 will be explained . the origin is generally set at the position of the ( 0 , 0 ) dot of the liquid crystal display board 25 , namely , at the left upper corner of the liquid crystal display dot . since the coordinate systems of the input tablet 21 and the liquid crystal display board 25 deviate a certain distance , the origins of them can be made in agreement by measuring the deviation amount and adding it to its ad value . if the ad value at the origin is denoted by ( adx o , ady o ), the coordinate value ( x n , y n ) of a point p n is as follows : the x . adx o and y . ady o of the second term of the right side in equations ( 3 ) and ( 4 ) are deviation amounts . these of x . adx o and y . ady o can be known by indicating , by pressing , onto the origin with the indicating pen 23 , but it can also be determined from the ad values of the above - mentioned p 1 to p 4 without pressing the origin over again . fig7 is one in which the horizontal axis shows coordinate values and the vertical axis shows ad values . as apparent from this figure , the magnitude of the above - mentioned deviation amount is the length of the cut piece 71 itself on the horizontal axis . to determine this algebraically , in practice , by taking into account an error occurring when p1 to p4 are indicated by pressing , ## equ5 ## from the above , the coordinate values of an arbitrary point p n from equations ( 1 ), ( 2 ), ( 7 ) and ( 8 ) are : therefore , in the case of this embodiment , correction parameters which are calculated from the result of a calibration operation are the following four kinds : incl x , incl y , offset x , and offset y . the calibration operation as mentioned above is generally performed at assembly time in a factory before shipment , so the user need not particularly be conscious of the calibration . however , after several months to several years from the date of the purchase , the resistance value of a resistance film undergoes a secular change , and coordinates deviate a little . therefore , the user himself has to perform a calibration operation as mentioned above . in the case of this embodiment , pressing a soft switch ( calibration key 61 ) of the rightmost end as shown in fig6 ( a ) enables the start of a calibration operation to be instructed . however , such calibration operation is not often performed , and therefore a proper execution of the operation will not necessarily be performed . in fig6 ( a ), for example , if a point p 5 is erroneously pressed instead of a point p 1 , its correction coefficient , unlike that of equation ( 1 ), is : ## equ6 ## in consequence of this , the deviation amount of the axis is : ## equ7 ## such calibration operation is primarily performed to match coordinate systems . if an indication position is mistaken as mentioned above , in consequence , there is a possibility in that the deviation or distortion of coordinates are made larger than before calibration . in the case of the prior art mentioned above , even if the system enters such a situation , the calibration operation can be started again by pressing the calibration button of the keyboard 91 , so no problem is posed if the operation is correctly performed the second time . however , in the case of an electronic apparatus having no input section other than the input tablet 21 as in this embodiment , even if the soft switch furtherest to the right ( the calibration key 61 ) shown in fig6 ( a ) is pressed with the indicating pen 23 to start the calibration operation again , this input is not accepted since the coordinate system of the input tablet 21 deviates greatly . therefore , the fact that the region of the calibration key 61 of the input tablet 21 is indicated with the indicating pen 23 cannot be recognized , with the result that the calibration operation cannot be instructed to be started . needless to say , this makes an ordinary use of the apparatus difficult . accordingly , in one embodiment of the present invention , the following configuration is adopted . that is , after the correction parameter is calculated , it is not definitely determined instantly . at first , as shown in fig6 ( b ), a message for prompting the operator to again press the calibration key 61 , which is a soft switch for calibration , is displayed . at this time , by using a newly calculated correction parameter candidate , the position of the coordinates pressed with the indicating pen 23 is calculated . a check is made to see whether or not the coordinate value thus obtained is a coordinate value corresponding to the region of the soft switch 61 for use in calibration . in other words , when the fact that the calibration soft switch 61 is pressed can be recognized , then , the correction parameter candidate is determined as a formal correction parameter . on the other hand , when a coordinate value corresponding to the region of the calibration soft switch 61 cannot be obtained , the correction parameter candidate is not determined , and the content of the correction parameter remains as before . that is , it follows that only in the state in which the calibration operation can be instructed to start when the calibration soft switch 61 is pressed , is the calculated correction parameter adopted . the above process will be explained with reference to the flowchart of fig1 . the control program for executing this process is stored in the rom 112 of the processing section 20 . when the input surface of the input tablet 21 is pressed with the indicating pen 23 , the operation proceeds to step s1 where the region pressed with the indicating pen 23 is determined . in step s1 , it is judged whether or not the region of the calibration key 61 is pressed with the indicating pen 23 . if there is no instruction from the soft switch 61 , the operation proceeds to step s2 where a process corresponding to the pressed key or inputting of the other coordinate values is performed . when the calibration key 61 is pressed , the operation proceeds to step s3 where , for example , as shown in fig6 ( a ), an indicated point p ( p1 to p4 ) is displayed on the liquid crystal display board 25 . next , the control proceeds to step s4 where the system waits for the operator to indicate each point . in this way , the system waits for the operator to press these displayed points , and after this is completed , the operation proceeds to step s5 . in this step , the pressed coordinate value is calculated , and a correction value for calculating a pressed coordinate position is determined on the basis of the deviation with respect to a corresponding position ( the position of the point p 1 , etc .) on the screen . then , this value is stored in the ram 113 as a correction parameter candidate . next , in step s6 , the message 62 , for example , that shown in fig6 ( b ), is displayed on the liquid crystal display board 25 so as to prompt the operator to press the calibration key 61 , which is a soft key . in step s7 , the system waits for a key input through the use of the indicating pen 23 . if an input by the indicating pen 23 occurs , the operation proceeds to step s8 where the coordinate value of the position at which the input tablet 21 is pressed is calculated by using the correction parameter candidate stored in step s5 . next , the operation proceeds to step s9 where it is determined whether or not the coordinate value calculated by using the correction parameter candidate corresponds to the position of the calibration key 61 . when the coordinate value calculated by using the correction parameter candidate is within the region of the calibration key 61 , the operation proceeds to step s10 where the correction parameter candidate is determined as the correction parameter during coordinate value calculation time . that is , this correction parameter is used during coordinate value calculation time after this determination . on the other hand , when the coordinate value calculated in step s9 does not correspond to the region of the calibration key 61 , the operation proceeds to step s11 where the correction parameter candidate is not adopted , so the correction parameter is not updated . in this case , the content of the correction parameter is left unchanged , that is , as it was before the calibration operation , and the system waits for a correct operation to be performed . as set forth hereinabove , according to this embodiment , since the correction parameter remains undetermined when the user has performed an erroneous operation during calibration operation time , the present invention has an advantage in that the input tablet can be prevented from going into an inoperable state after its input coordinates deviate greatly or are distorted . in order to instruct the calibration operation to start , an ordinary pop - up menu or a pull - down menu , rather than a separate soft switch as mentioned above , is provided . for example , as shown in fig8 ( a ), when a soft switch of the &# 34 ; menu &# 34 ; 81 is pressed with the indicating pen 23 , a menu 82 having three soft switches , &# 34 ; clear entire screen &# 34 ; &# 34 ; thick pen / thin pen &# 34 ; and &# 34 ; calibration &# 34 ; is pop - up displayed on the liquid crystal display board 25 . at this point , to instruct the calibration operation to start , the surface within the frame 83 is indicated by pressing continuously . the calibration operation at this instance is , for example , as explained with reference to fig6 to determine the correction parameter candidate by displaying points p on the screen 25 and specifying each point with the indicating pen 23 . when the correction parameter candidate is calculated in this way , the region of the &# 34 ; menu &# 34 ; 81 is pressed in accordance with the instruction in fig8 ( b ). then , the surface of the soft switch &# 34 ; calibration &# 34 ; within the frame 83 is pressed in accordance with the display of fig8 ( c ). only when the coordinate value calculated by each input pressed corresponds to the region of the soft switch of the &# 34 ; menu &# 34 ; 81 and the surface of the soft switch &# 34 ; calibration &# 34 ; within the frame 83 , is the correction parameter candidate definitely determined as the correction parameter . of course , if the adoption of this correction parameter candidate is determined by only repressing within the &# 34 ; menu &# 34 ; 81 , the advantage of the present invention is not lost . as described above , the predetermined region and its pressed input referred to in the present invention are not limited to one pressing point . this region also includes a case where a plurality of pressing points are in turn pressed , or where they are all pressed at the same time . in the above - mentioned embodiment , the explanation was made taking one of the resistance file system used as a coordinate input section as an example . however , the present invention is not limited to this embodiment , and it goes without saying that any of those apparatuses which accept coordinate inputs by indicating on a tablet surface with a dedicated pointer an ordinary writing tool , or a finger can be widely used irrespective of their principles or systems . as set forth hereinabove , according to the present invention , since a correction parameter remains undetermined when the user has performed an erroneous operation during calibration operation time , the calibration operation can be safely updated and an apparatus can be prevented from becoming inoperable due to an erroneous operation . in addition , since the instruction to recalibrate can be given at any time regardless of the success or failure of the calibration , the user can perform the calibration operation without any fear of making making errors and feeling at ease . further , the present invention has an advantage in that , after it is determined whether or not a correction parameter is adopted , the determined result is displayed , and thus the user can recognize the success or failure of the up - to - date calibration operation . as many apparently widely different embodiments of the present invention can be made without departing from the spirit and scope thereof ; it is to be understood that this invention is not limited to the specific embodiments thereof except as defined in the appended claims .