Instrument for facilitating the calculation of equivalent values
BACKGROUND OF THE INVENTION 
     The present invention concerns an educational aid which facilitates the calculation of equivalent values. 
     The object of the invention is to make it easily possible to indicate exactly in writing a measurement of the decimal metric system for indicating the dimensions of digits and for the rapid transformation of one measurement into an equivalent one. 
     As will be clearly explained hereinafter, this educational aid facilitates the learning of the decimal metric system, since it visualises the dimensions of digits. 
     The educational aid, hereinafter called a &#34;rule&#34;, enables a child, by means of its use, to record the value of the symbols and the serial arrangements thereof within the field of comparison in an almost play-like form. 
     The present invention will be described with reference to the decimal metric system having a base of ten, but it may also be applied to other metric systems having a base different from 10. 
     Other objects of the present invention will become apparent in the course of the following description, to be taken into consideration, together with the attached sheet of drawings, in which some preferred embodiments of the invention are shown. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a plan view of the rule, with a slide having a pointer in a partly extracted position; 
     FIG. 2 is an exploded view showing the various parts of which the rule is composed; 
     FIGS. 3 and 4 show the front and back of a rule for the measurement of surfaces and volumes; and 
     FIG. 5 shows a plan view similar to that of FIG. 1 of the rule in which the pointer is linked to the displacement of a slide. 
     Like referenced numerals and letters used in the Figures refer to identical or equivalent parts. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIGS. 1 and 2, it can be seen that a rule is composed of a substantially rectangular front plate 6, suitably of plastics material, in which a rectangular window 7 is formed, and a back plate 8, also provided with a window 7, securable to plate 6 by means of press studs 9 engaging in suitable recesses (not shown) provided on the back of the plate 6. When the plate 6 and the back 8 are assembled a slide 10 is supported between them, on which slide 10 a pointer 11 is provided. The slide 10 has a longitudinal rib 12 which is guided within a suitable guide slot 13 formed in the back surface of the plate 6, and terminates in a substantially rectangular handle portion 14 capable of being received in a suitable recess 16 provided on the back of plate 6 and partly visible in a window 15 of the plate 6. The handle 14 is provided with notches 17 to facilitate gripping of the handle 14 and manipulation of the slide 10 after it has been extracted from the recess 16 by acting on curved ribs 18 provided on the front of the handle 14. The ribs 18 also provide seats for engagement of an end portion of a strip 19 adapted to slide on the outer surface of the plate 6, in a suitable recess (not shown) provided below the window 7. The strip 19 carries symbols representing powers of units indicated at 20 by &#34;uM - hk - dak - uk - h - da - u&#34; on the left of the pointer 11 and by &#34;d - c - m&#34; on the right of the pointer 11. These symbols are in practice those of units of measurement, and may also be different from those indicated, which in fact represent: uM = unit of millions, hk = hundreds of thousands, dak = tens of thousands, uk = units of thousands, h = hundreds of single units, da = single tens, u = single units, d = tenths, c = hundredths and m = thousandths. 
     From the above, it is clear that the symbols of the power of the units have to be displaced at the same rate as the pointer 11, or they have to be linked to the displacement of the pointer 11, and therefore it is obvious that, instead of being engaged on the ribs 18 the strip 19 can instead be connected to the pointer 11 without altering its essential characteristics of the apparatus. 
     Above the window 7 a series of symbols of the units of length, weight and capacity are indicated by 21, 22 and 23 and are separated, symbol by symbol, by means of lines, each line being distinguished by a letter of the alphabet from A to M. In addition to this, the upper part of the plate 6 is provided with two arrows under which the words &#34;left&#34; and &#34;right&#34; are written, which indicate that, if the pointer is displaced to the left, a specific measurement is converted into a corresponding one by means of a division, see also the sign of division (:) above the arrow &#34;left&#34;, whilst, if the pointer is displaced to the right, a specific measurement is converted into a corresponding one by means of a multiplication, see also the sign of multiplication (x) above the arrow &#34;right&#34;. 
     The rule is used in the following manner: 
     When an operator wishes to write in the window 7, on a piece of paper below it, the measurement 415 units of meters (415 m), the operator must, first of all, displace the pointer 11 so as to align it with the line H, so that the symbol u is disposed below the symbol m, and then write the digit 5 between m and u, the digit 1 between dam and da, the digit 4 between hm and h. 
     When the measurement 415m is to be transformed into an equivalent, for example in cm, the operator simply displaces the pointer 11 to align it with the line L and to add zeros below the symbols dm and cm. It is obvious that the displacement of the pointer 11 has also caused the displacement of the symbols of the powers, whereby, with the equivalent value computed, the digit 4 will no longer be between hm and h, but between hm and dak. This fact shows the positional value of the digits unequivocably, since, before the conversion, the digit 4 had the dimension of hundreds of meters, whilst after the conversion, the digit 4 has assumed the dimension of tens of thousands of centimeters. 
     On the other hand, if the pointer 11 had been displaced from the initial position, in alignment with the line H, to the left to become aligned with the line F, another conversion would have been performed, i.e. from m into hm, always with the result of showing the new dimension of the digit 4 which, becoming disposed between hm and u, assumes the value of 4 units of hectometers whilst the digit 1 becomes tenths of a hectometer and the digit 5 becomes hundredths of a hectometer. 
     Obviously, therefore, the pointer 11 always signals the end of a whole number and the end of the whole part of a number which has a decimal part, and in such a case the pointer indicates the place where normally the decimal point should be. 
     With reference to FIGS. 3 and 4, it may be noted that both sides of the rule may be used. FIG. 3 in fact shows the units surface area 24 in their proper order, whilst FIG. 4, the back of the rule, shows the units of volume 25 in their proper order. These Figures do not show the symbols for units of quantity for indicating the power of the digits, but it is obvious that this fact in no way alters the substance of the invention, since such arrangement must obviously reproduce the visual representation of the dimensions of the digits, as described for FIGS. 1 and 2. 
     The rule shown in FIG. 5 is similar to that of FIG. 1, and it is evident that the pointer 11 is connected to two parts 26 and 27 of a sliding cursor adapted to move in suitable grooves or on ribs provided along the upper and lower sides of the rule. This cursor made, for example, of transparent plastics material, and may obviously be provided with extensions for carrying the symbols for indicating, as in the case of the rule in FIGS. 1 and 2, the dimensions of the digits. 
     In FIG. 5, the extensions of the cursor for carrying the symbols of the dimension, instead of being outside the window 7, as in FIG. 1, are inside the window and it is clear that they may be located above or below the space for writing the numbers. 
     It is thus apparent from the above description and drawings that the calculating instrument of the invention is capable of converting a numerical value of a given quantity in one unit to a numerical value of the same quantity in a different unit. The plate means 6 thus carries a series of scales such as the scales 21-23, in each of which different units of a given quantity are arranged in the form of graduations of the scale which are situated at a given distance from each other. Thus the scale 21 has its graduations arranged according to different units of distance or length, while the scale 22 has its graduations arranged according to different units of weight, and so on. The plate means 6 has operatively connected thereto, for movement in a direction parallel to any one of the scales 21-23, the scale 19 which has thereon the series of graduations 20 indicative of different characteristics of a numeral, these characteristics in the illustrated example being the arrangement of the digits of the numeral according to the tens or decimal system. The pointer 11 is operatively connected with the movable scale means 19 for movement therewith and is situated at a part of the scale of graduations 20 according to which the part of the numeral which is on one side of the pointer 11 will have a given relationship with respect to the part of the numeral which is on the other side of the pointer 11, this relationship in the illustrated example being such that on the left of the pointer 11 the part of a given numeral extending up to its decimal point is arranged while on the right of the pointer 11 the part of the numeral subsequent to the decimal point is arranged. Of course the graduations of the scale 20 are situated with respect to each other at the same distance as the graduations of any one of the scales 21-23. 
     The plate means 6 includes a means for situating initially a given numeral with respect to one of the scales 21-23 so as to be indicative of the quantity represented by the selected one of these scales in a given unit. This means for situating such numeral with respect to a selected one of the scales 21-23 is of course formed by the window 7 behind which a sheet of paper may be situated so as to have the initial numeral written thereon. After the pointer 11 is aligned with the numeral thus written initially on the paper behind the window 7, it is of course possible to shift the pointer 11 and the scale 19 therewith, in the manner described above, so as to be able to convert the numeral representing a given quantity in a given unit into a numeral representing the same quantity in a different unit. 
     Within a practical embodiment of the present invention, any formal variations may be made which do not alter the substance of the present invention and may therefore be considered as falling within the scope of the invention. 
     It is likewise evident that the material for producing the rule may be of any type, such as plastics material, cardboard, synthetic fibres, wood, metal and the like, or any combination of these materials, without thereby departing from the range of possible embodiments of the invention.