As noted in this post the AquaCheck Select/7-way do not measure Calcium Hardness, but rather Total Hardness, so if your numbers came out close then your magnesium level is probably low. If you had hard water, then you'd more likely see the test strips measuring a higher number than the actual CH.
How can the test strips measure "right on the money" when they only give ranges of 0, 30-50, 100, 150, 300 for the CYA test? Even when such tests are working, they are just ballkpark estimates. The chlorine test for our usual ranges is something you might get to with 1 ppm FC at best; with TA it's 20 ppm at best; CH if there is no magnesium to within 125 ppm at best; and CYA to within 50 ppm at best. Since the control of algae by managing the FC/CYA ratio is rather critical, I don't see how one could do that only knowing that the CYA is "between 30-50 ppm" and "100 ppm" since that's the size of the jump in that test. Maintaining, for example, 3 ppm FC with 30 or 40 ppm CYA is fine but at 60-100 ppm CYA then algae could grow (for a manually dosed pool).
Basically, using a colorimeter to get rid of the visual matching errors could get the FC measurement in decent shape to within 0.5 ppm and the pH test could be OK as well, but the other tests are more dicey even with an instrument, especially for CH that isn't measured at all and for CYA (TA is sort of OK if an instrument can get the accuracy to around 10 ppm -- it's not clear if it could).
How can the test strips measure "right on the money" when they only give ranges of 0, 30-50, 100, 150, 300 for the CYA test? Even when such tests are working, they are just ballkpark estimates. The chlorine test for our usual ranges is something you might get to with 1 ppm FC at best; with TA it's 20 ppm at best; CH if there is no magnesium to within 125 ppm at best; and CYA to within 50 ppm at best. Since the control of algae by managing the FC/CYA ratio is rather critical, I don't see how one could do that only knowing that the CYA is "between 30-50 ppm" and "100 ppm" since that's the size of the jump in that test. Maintaining, for example, 3 ppm FC with 30 or 40 ppm CYA is fine but at 60-100 ppm CYA then algae could grow (for a manually dosed pool).
Basically, using a colorimeter to get rid of the visual matching errors could get the FC measurement in decent shape to within 0.5 ppm and the pH test could be OK as well, but the other tests are more dicey even with an instrument, especially for CH that isn't measured at all and for CYA (TA is sort of OK if an instrument can get the accuracy to around 10 ppm -- it's not clear if it could).