This is probably the third of at least three Computation Units. Earlier versions appeared in 1951 (unit 123) and 1958 (unit 209). The unit includes:
This unit is an updated edition of unit 209, which contained a longer slide rule and a shorter booklet, but is otherwise identical. The final pages of this unit's booklet contain a description of binary arithmetic, including 6 experiments (exercises), which were not in unit 209.