There is a calibration set up in Easel. You go to General Settings/Machine Inspector where you’ll see the console line. You just type in $100= ( your new number). Repeat for $101 and perhaps $102.
Now this setting number is just a ratio of “what you want” to “what you are getting” and multiplied by the current number that is in the setting now.
So let’s say you tell the machine to move 1". and it moves 1.100". The ratio is 1/1.1. You do the math . .9090 is the result. You mulitply .9090 by the setting number currently in Grbl. For example we will use 40 in the settings now. 40 times .9090=36.364. You would go to the console and type. $101=36.364 and hit enter. That’s how it is done. If you use a caliper and do this a few times you can really get close to being accurate within a few thousandths, assuming everything else is adjusted properly and you have the upgrades.
Here are the GRBL settings and what they do.