The Taylor titration tests are plus or minus one drop, so the counting drops FC & CC tests are +- 0.5 or 0.2 depending on how you are doing the test, while TA & CH are generally +-10 (+-25 when drops count as 25). The PH test, and color based TC, FC, & CC tests, depend a great deal on experience and how well lit the sample is. For PH that is generally +-0.1 but with experience and very good lighting it can be read more precisely than that, and with bad lighting it can be +-0.2. Likewise the color based TC, FC, & CC tests can generally be read to within half the step in the color standard you are using but may be more or less precise depending on experience and lighting. The CYA test is less precise at the ends of the scale. CYA levels can actually be dramatically high when the test reads around 100, and levels below 25 can often read as zero.
CYA testing only needs to be done when you have some reason to suspect that the level has changed. I read it first thing in the spring, one week after adding any CYA, and any time there may have been significant water replacement (for me backwashing and rain typically require one additional test about two thirds of the way through the season). If you have a SWG and are measuring the salt level, salt measurements can be used as a proxy for the CYA level as salt and CYA generally move together (both are primarily affected by dilution during the season).
