Make a sketch of the drip line layout showing the lateral lines with drippers, dimensions of the zone and locations where the catch cans are placed. Take photos with the digital camera.
Catch cans should be placed to give a representative sample of the uniformity of the area. For a growing bed with several laterals lines running full length, catch cans four or more places down each of five of more laterals will give an indication of the overall uniformity of watering of the growing bed. Spray stakes can be placed into the catch can. Drippers in lateral lines can be placed on top of the catch can if the catch can is not too tall. Otherwise a short squat can may be needed. The volume should be large enough to catch the water from one watering cycle.
In a large growing bed the uniformity might be sampled by doing a uniformity test near the beginning of the bed and near the far end of the bed. Each test would show the uniformity of the emitters at each end and then the results of these tests can be compared to see what the difference in distribution is between ends of the bed by comparing the average values. If elevation difference is a factor, it is likely that a non-pressure compensating emitter would show the difference in pressure loss (friction) and elevation.
Again, on the site map show the location of the drip laterals and emitters. Show the location of the catch cans. Allow room to write in the data measurements.