Decimal numbers between 100 and 109 would be represented in BCD by the actual number + 156 (26*6). Numbers between 110 and 119 convert to BCD values of the actual number + 156 + 6.

The button inputs are interpreted as binary, which he can then convert to decimals, and… Well, it’s about here that I stop grasping how any of it works, but the results are undeniably impressive.

LEGO binary to decimal conversion [Carl] is doing a few experiments to see if it’s possible to build a calculating machine out of LEGO. He managed to convert four bits of binary into decimal.