The 20R has similar functionality to the 18R, but the equals key is moved to a more 'modern' position, and the memory functions are enhanced so that one may add, subtract, multiply and divide the displayed value to the memory. There are no markings on the 20R to indicate this operation, but this seems to have been rectified in the 21R, which has exactly the same functionality. One major enhancement over the 18R is the fact that all 8 digits are used for negative numbers. The minus sign is displayed on a ninth digit on the right (which is slightly odd). This ninth digit also indicates an error condition (such as overflow) by displaying 'E' and (more usefully), the decimal place is lit when the memory register is non-zero, so one no longer has to remember if there's a value stored there.
This particular calculator has its I.C. labelled 7508 (1975 week 08). The manual for the 21R (identical functionality to the 20R) is available on the manuals page.
Try it out---it works!
<- Prev Page Next Page->