Heads don't roll on this forum. (except maybe for those of "poolstore" salespersons )

The FAS/DPD test goes like so
put an amount of pool water into a test tube
add a tiny scoop of a powered dye, it will turn the water red/pink
add a reactant a drop at a time and swirl to mix between drops
suddenly on one drop, the pink goes clear ... done
depending on the kit you use the # of drops to calculate the free chlorine, usually by dividing by 2 eg. 7 drops = 3.5 Parts Per Million ( PPM ) of free chlorine.

That's only half the story though. You need also to find you "combined chlorine" levels. Combined chlorine was at one time, free chlorine in the pool. It has partially reacted with organics in the pool ( worms, leaves, grass, insects, kids pee etc) and has partially oxodized them. This is the source of the stinky chlorine smell you will find around a lot of pools, especially commercial or public pools. It forms this intermediate step because the free chlorine levels were not quite high enough to finish the reaction. So we test for it. If we find much of it we know the job has not quite been done. The solution is, strangely enough, jack up the chlorine levels. This is called shocking. Shock is not a product, but lots of pool stores like to sell stuff that is labelled shock. Shocking is simply bringing up the free chlorine levels to finish the oxodization and eliminate combined chlorines.

So the second half of the test is to discover you Combined Chlorine (CC) level. The FAS/DPD kit has a 3 dropper bottle to do this test. Again it is a clear solution or red solution result and easy to read. If you CC is 0.5 PPM or greater, you increase your chlorine levels for a day or so ... until the CC is back below 0.5 PPM

The kit that Ben sells here has both the easy "shades of yellow/pink/red" test , (aka OTO test) that you say you have problems reading. By the way it is widely believed that women can read that color test better than men. Ben's kit is a great package. His delivery is a bit slow at times. You can also get a pool store to order an FAS/DPD kit for you.

Hope all this helps.