This confirms what everyone has told me all along, even the pool store guys. The test is totally subjective. However, the condition of the testing tube (yellowed and tarnished vs. clean and clear) has to be added to the list of variables.

My expeience showed the "Pool Store" reading be higher than actual, and thus taking away the "Need" to buy more chemical.

So this kinda works in reverse. It would behoove the pool stores to use new or clean testers in good lighting in order to sell more CYA.