Hi and welcome!

Just to add to WM's advice: Don't use the 25ml line for your testing of chlorine (FC and CC). Instead use the 10ml line. That way, each drop of the R-0871 liquid will equal .5ppm of FC or CC, and 2 drops = 1ppm. Whereas, with the 25ml line you need 5 drops for every 1ppm--and that uses up your reagent liquid. Measuring to .5 rather than .2 is 'WAY good enough for everything we do here.