I weighed my first shot today and very happy with the results!
18g double basket for a 30.1g espresso in 28 seconds.
I used a small digital scales (wrapped in glad wrap) and zeroed it out with the empty cup.
I think I had probably been pulling 20ml shots and thinking they were 30 and therefore my timing and hence grind, tamp etc was out.
Such a simple solution* to a problem that has been bugging me for a while!
*making no claims to this as my own solution of course!
It is a good way to do it
I found after a bit of testing that at a pour rate on 1ml per second the weight of the extraction in grams is equal to the quantity of the extraction in mls. So now I uses the scales and a measuring glass to tell the quality of the extraction