"The 1857 NYI Annual Report mentions how blocks like these are used when placed side by side represent arithmetical computations.
"For the sake of simplicity the types are made by their different positions to correspond to the Arabic numerals. A type having at one end the letter T, at the other the letter V, represents the final eight figures. Another represents at the one end by the letter L, the figure 9; at the other, by a blank surface, zero, completing the decimal series. Thus:
By this simple and beautiful method all the ordinary calculations are effected. Each frame needs sixty type over which the fingers move with celerity and precision. "
Twenty-first Annual Report of the Managers. 1857.P 12-13