Many bartenders use a glass for mixing their drinks, which works well and is relatively cost effective – you can buy very beautiful Japanese mixing beakers online. I use metal birdy mixing tins made by bartender Eric Lorincz. Metal chills drinks much faster and more consistently than glass, and even though you can’t see the liquid inside, with time you get to know how much you need to stir to get the dilution required. Essentially, I think if you are consistent and use the same equipment to make the drink you will learn how to get the desired result.