The capped part is calculated from the law: 0.2% on UK consumer debit, 0.3% on UK consumer credit. Everything else comes from your own statement, because nobody can honestly guess it for you.
The capped lines use the statutory caps of 0.2% and 0.3%, which apply when merchant, acquirer and issuer are all in the UK. Commercial and cross-border cards sit outside those caps, so that line takes the rate from your statement rather than inventing one. Defaults are placeholders, not a benchmark.
Do not know your scheme fee or markup separately? That is a blended contract, and lesson four is about exactly that.
Read lesson 04