Weighing yeast starter

I made my first yeast starter yesterday with the fist yeast I washed. Of course I was worried that the yeast wasn't viable or I'd screw up the starter etc... I'm not using a stir plate, just shaking every time I walk by so krausen doesn't have much of a chance to form to see if things are working. I thought I'd try weighing it to see it's progress, and calculated it should loose about 30grams through fermentation, so far it's down about 15.
Is this a reasonable was to monitor a starters progress, I've seen the question asked a lot but haven't seen much of an answer.

Haha nice use of stoichiometry. To be honest I've never thought about it, but it should work. Most people just measure the gravity though.

You should see a good bit of CO2 come out of solution when you swirl it, and it should froth up a bit. At least I used to before I built my stir plate...