These are the rules, folks. Love 'em or leave 'em. (Seriously, you can leave 'em.)
Never add more than a thimble’s worth of vermouth to a dry martini. For those without a sewing kit, it's acceptable to rinse out the glass with vermouth; the “legs” that run down the glass will be enough.
OK, yes, less is often more. And you’ll certainly save money on vermouth by being stingy with it. But there is no disgrace in ignoring this rule. It’s based on a misunderstanding of what “dry” means.
Dry does not mean “keep the vermouth in the cupboard.” Here, as with wine, the opposite of dry isn’t wet; the opposite of dry is sweet.
And a dry martini is, essentially, a martini with dry not sweet vermouth in it.
Incidentally, for anyone attempting to mix a top-notch martini, these additional definitions of "dry" are also instructive:
“Not yielding milk.” So true, and I would extend the definition to include yoghurt, sour cream...basically, no dairy products of any kind should be yielded.
“Served or eaten without butter, jam, etc.” Yes, certainly.
"Plain or unadorned.” If you’ve slipped a diamond engagement ring into someone’s martini, it's technically no longer dry.
At any rate, in pursuit of my own personal perfect martini, I’ve gone from one extreme to the next where the vermouth is concerned, from the austere -- rinsing out the glass with vermouth (swirl and dump) -- to the extravagant: using equal measures of vermouth as gin (which is way too much vermouth for my tastes).
From this extreme of equal parts, I gradually pulled back on the vermouth by slight measures until I hit it just right. Unfortunately, I can’t tell you what that perfect amount is. There’s this nick on my shot glass, and I fill the vermouth to the top of that nick. My science is not exactly exact.
Bottom Line: If you prefer a little more dry vermouth in the mix, go for it. It's not the wrong way to make a martini. Five-to-1, 4-to-1, 3-to-1...preference is a personal thing. Everybody’s gotta find his own nick.
A few martini recipes to fiddle around with: