I'm working on the accuracy of the stop-watches. First I performed some tests and It seemed that a lot can be improved in many areas (I'm writing an article about the process). The most important part was to use a proper temperature controlled oscillator (TCXO) which you can see below. The canned 8MHz crystal is not used right now. I'm getting 1ppm accuracy against my bench signal generator, but the final test would be to test the system against a GPSDO which is about 0.01ppm accurate. Oh, and the least precise element is the IR trigger, but still, I'm getting ~100µs precision out of it (in the lab environment).