FWIW, aus dem Link in #5 :
... What Is Dialling In?
... The phrase “dialling in” is used to describe the process of making espresso taste as delicious as possible. Essentially, you are looking to extract the right amount of soluble flavour from the coffee using the right amount of water.
In order to achieve this, you must change the parameters of the espresso. The three main parameters are the dose, yield and brew time, all of which have a massive impact on flavour.
When dialling in, you should only adjust one parameter at a time, otherwise you can easily lose track of which has affected the espresso’s flavour in a certain way.
Extraction levels are also important when it comes to dialling in. When not enough coffee extracts into the water – under-extraction – the espresso often takes on a sour taste and a viscous consistency. If too much coffee is extracted, however – over-extraction – then the espresso can taste dry, bitter, or burnt. ...