Thanks for all the creative alternatives - I have used them all. Trying to get a little more precise than "the finger" or "the weight" because I think I may be over-watering but wanted a more precise measurement. This is a useful toy sold in most hydro and other gardening stores. I paid $9. Also has a handy-dandy light meter on it. While not useful for absolute light, it is quite useful for comparing the intensity of 1-2" from a CFL, then setting a proper MH height to match in order to lessen light shock.