Thanks a million for the great article. I got hold of a meter in good shape except for a sick photocell. I substituted a cell from a dead Gossen meter and followed your diagrams to build a circuit board. My cell has a different response slope so I had to change two of the fixed resistor values to get the calibration into range. After an hour of back and forth tuning the high and then low ranges it turned out to be amazingly accurate. It's within 1/2 stop of the readings from my Lunapro SBC reference meter over the top 4/5 of the scale on both ranges. I'm waiting for the weather to warm up so I can go out and play with it.