If you have high CH, use a 10 ml sample. Saves time and reagent, and realistically, do you really care if the reading is 610 or 625? It's close enough.
If you expect that your CH level is extremely high, you can do the test so that each drop is 25, instead of 10, to speed up the process and save on reagent usage. Use 10 ml of pool water, 10 drops of R-0010, 3 drops of R-0011L, and multiply the number of drops of R-0012 by 25 to get your CH level. http://www.troublefreepool.com/extended-test-kit-directions-t25081.html