# User:Steven J. Koch/Notebook/Kochlab/2009/07/10/QPD debugging

### From OpenWetWare

- the code I added last night did not work. That's because I stupidly divided the integer value of the QPD X by the integer value of the QPD sum and did not multiply by any factor. So I gotta fucking fix that. Best idea is to use a global variable for a scale value that will make it behave like the On-Trak. For the On-Trak, we had:
- 7.17 mV / nm (for 500 micron beads)

- @ 350 mW, the sum signal is 3.96 V. And the X signal was about 0.333 mV / nm.
- 0.333 mV / nm / 3960 mV = .000113 nm^-1
- If we multiply this number by 2^16, we will get 7.3728. This is such a coincidence (given we have a 16 bit board, and are storing 32 bit numbers) that I'm just going to do it for now.