It looks like DTL (diode-transistor logic) is being used; if implemented properly, quite a few parts are needed for just a NAND gate, and a BCD decoder uses a l

It looks like DTL (diode-transistor logic) is being used; if implemented properly, quite a few parts are needed for just a NAND gate, and a BCD decoder uses a lot of them. That said, counters aren't lightweight in that arena either...