Actually, keeping track of what you add with dichlor and trichlor is pretty easy. Here's how:

1. Figure your PF, which is the ratio of a million pound pool (120,000 gallons) to your pool => 120/20.1 = ~6

2. So, if you add 1 lb of chlorine gas to your pool (100% chlorine) you add 1 x 6 ppm to your pool. If you use dichlor (56% chlorine) you will add 0.56 x 6 or ~3 ppm chlorine.

3. BUT, both trichlor (90% chlorine) and dichlor (56%) chlorine are about 50% stabilizer. I know those numbers don't add up; the answer lies in some old potable water treatment history that I'm not going to drag out, but it's not a typo

4. SO . . . if you add 1 lb of EITHER dichlor or trichor to your pool, you wll have added 0.5 x 6 or ~3 ppm CYA to the pool. Put it another way: if you buy this shock:
Kem-Tek dichlor 12 lbs @ Amazon => ~$4.00/lb (Jul 2013)
and use it in your pool, you will have added 12 x 0.5 x 6 ppm CYA to your pool, or 36 ppm, MINUS whatever water you have lost to backwashing or splashout.

SO . . . all you have to do is put a chart with your chemicals, and keep a record of every time you buy more dichlor or trichlor. Take the pounds, and multiply pounds x 50% CYA x PF to find our how much you've added.