1. This rule was made in former Eastern Germany.
2. The front of the rule is a simple straightforward design.
3. The back of the rule has two pairs of scales which I have not seen elsewhere. At the bottom (confusingly labelled C and D) are two linear scales from -12 to +12. These have no marked subdivisions between the integer values and can be used for a limited range of addition and subtraction. Also on the back, inverted relative to the name of model of the rule and the previous scales (and also even more confusingly named C and D) which run from 0 to 25 with intermediate values of 0.1 marked. These can also be used for addition and subtraction. It would appear that this rule introduced the idea of addition and subtraction of numbers using distance scales as a prelude to performing multiplication and division by using logarithmic scales.