I would somewhat qualify what was said in the link about how to do the CYA test. You want to mix for 30 seconds (longer is OK, but not necessary) -- no need to shake as you don't want to create lots of bubbles, you just want to mix back-and-forth, back-and-forth, turning it one way, then the other, then back again. The temperature of the water should be around room temperature (normal pool temp is usually OK -- if the water it too cold, then the test may not fully develop in 30 seconds).
As for viewing the tube, I talked to Taylor about this a while ago and the measurement is closest to being correct when you hold the tube in front of you looking straight down (around waste level) with your back to the sun so that the tube is in bright indirect light (if you have to do the test indoors, create bright indirect light). If you view the tube with you facing the sun or the tube otherwise in direct sunlight, then you'll get a reading that is around 10 ppm lower and probably not as accurate, but keep in mind that the test isn't perfect anyway and at least +/- 10 ppm. Nevertheless, performing the test consistently in technique gets you pretty consistent results.
Richard