Abstract: One face of a tablet is divided into a plurality of adjoining regions. The two edge regions at the right and left have rows which in each region are divided into a plurality of fields and are numbered continuously with primarily basic numbers and their multiples, from one edge region continuing into the next. A number of slides, equal to the number of rows in each of the edge regions, lie loosely on the tablet, so that each slide may be pushed along the corresponding two rows which are at the same level of the edge regions in order, as desired, to thereby at least partially cover one or the other of these rows, so that the result of an arithmetic operation carried out in one or the other region can be read from the exposed field adjacent the end of the corresponding slide.