Just a FYI comment. I've been perusing the OLD "Pop 'Tronics" and "Radio-Electronics "(R-E) mags, (from 1970 and later, and found several circuits I have built in the past, and now can DOCUMENT!) But of Interest: 1. The February 1972 issue of R-E announced Fairchild had just released the µA741 op-amp in the 8 Pin DIP configuration (as opposed the existing 14 pin DIP case) and it sold retail for $4.85 in single quantity. 2. In the June 1972 issue, the "MAN-3" LED readout was announced, and only(??) $12.45 each. I guess things have changed a bit?