Our app note says to test each unit. But if your 'glass' is consistent and the airgap between the sensor and glass is small, you can get away with testing the first bunch off the line and using the WORST (largest) set of calibration numbers you come across.
The reason we pick the largest values is that if you are wrong you will slightly over-range. But if you choose a number that is too small, you will end up seeing 'ghost' (non-existent) targets in addition to under ranging.
If your glass is pretty good (and it looks it) and your gap is small the calibration really doesn't come into play until your target is small, dull, or far away. As the target gets closer the number of photons from the target will overwhelm those from the glass, and you will get a good answer even with a too-large crosstalk setting.
Slightly over-ranging at the far distances is much preferred over seeing a ghost image. And as you get closer, the number is more accurate.
One really should do the offset calibration on each unit however. There seems to be a lot of variability in that number.
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