I don’t measure while I draw anymore. I find it halts the process of drawing too much and creates a since of mistrust in yourself.
I feel that my drawings became truly better when I began trusting myself to put down proportions correctly and I stopped holding my pencil up to the model to measure widths and heights. I still do quick comparative measurements with my eyes where I imagine vertical or horizontal lines and place landmarks where they fall.
But when I finish a drawing and it’s obviously wrong, I begin to second guess myself on the whole measuring thing. So maybe I’ll go back to every now and then and use it as a tool to check my work. Not rely on it throughout the entirety of the drawing but in spots where I’m having issues.