I took nine samples of three level tablespoons -- trying for as much consistency as possible -- of the coffee I'm using right now (Scarlet City Warp Drive) and weighed each one in turn. Here are my results in grams:

- 17.3
- 18.2
- 17.3
- 16.9
- 16.7
- 17.4
- 16.9
- 16.9
- 17.6

So the average dose was 17.24g with a standard deviation of .464 g, and a maximum deviation of 1.3 g. I'll leave it to others more experienced than I to interpret the import of this, but I can say from experience with my lever machine, that a .4 g variance around 17g will necessitate adjusting the grind for optimal results.

FWIW, my take is that a decent scale is practically a necessity for dialing in the shot, and especially if one changes coffees from time to time.