Espresso is defined by a ratio: the weight of liquid in the cup divided by the weight of dry grounds in the basket. A classic shot is 1:2 — 18 grams of coffee yielding 36 grams of espresso.
Weigh both. Guessing by the cup's fill line is the single biggest source of morning-to-morning inconsistency.
At a 1:2 ratio, an 18 g dose should yield how much espresso?
Which habit keeps your ratio consistent morning to morning?
Ask your teacher anything that's unclear about ratios.