Dose, yield and time
Dose is dry coffee going into the basket. Yield is the mass of espresso in the cup. Time is an observation that helps compare shots. A 1:2 espresso ratio means twice the dose as beverage output; it does not mean adding twice the dose as water to a reservoir.
A starting point, not a target to obey
An 18 g dose and 36 g yield illustrate the arithmetic. Your basket, coffee and machine may call for a different starting point. Use a basket-appropriate dose, keep it consistent and change one variable at a time. Taste matters more than making every shot land on one number.
Plan the whole workflow
Look at grinder adjustment, basket compatibility, clearance above the drip tray and the sequence for making milk drinks. Leave space for knocking out grounds and wiping up. A machine that fits the counter may still be awkward beneath a low cabinet.
Know the equipment limits
Use the equipment manual for operation, cleaning and pressure-related procedures. Do not assume accessories fit because a nominal basket diameter matches. A useful setup is one you can maintain and use without fighting its dimensions every morning.
