I've been wondering this for a while. I currently have a TAG weather station to gather the data. I'm watching Temp, RH, BP, \and DA for all 4 cars. 3 on alcohol and the 4th on pump gas.

All I've ever heard about in the past was DA this and DA that. Then, I read the instructions for the TAG and it says the Vapor Pressure reading would be for Alcohol motors. I've never heard of VP until this.

However, I keep hearing people referring to water grains and some say this is one of the most important things to watch when trying to dial a car on Alky.

SO, what should I be looking at to get the best chance of understanding how it affects the cars?

My Tag won't do WG's so is there a stand alone meter that will or should I just bite the bullet and get a Kestrel?