By combining 49 of them he’s put together a soda bicarb diode steering circuit for a 7-segment display ... using a 555 and a 4017B decade counter to make a display count down to 0.

then latches the total to the 7-segment displays before zeroing the counter block and starting over. Six 4029 decade counters give the device a range of 1MHz. A set of 4511 BCD to 7-segment ...