Learn Dutch: Tijdens het controleren van de berekening heb ik me verrekend. - While checking the calculation, I miscalculated.

This is a specific Dutch pattern. Adding the prefix ver- to a verb and making it reflexive (like zich verrekenen) often expresses doing that action incorrectly. Here, it turns calculating into making a calculation error, with me acting as the reflexive pronoun for ik.

Can I turn any verb into a mistake by adding "zich ver-" to it?

Not every verb works this way, but it is a very productive pattern to learn. Other common examples include zich verslapen (to oversleep) and zich verstappen (to misstep). Whenever you see a reflexive verb starting with ver-, there is a good chance it means the action went wrong.

Why does the sentence use "Tijdens het controleren" instead of a clause like "Terwijl ik controleerde" (While I checked)?

Placing het before an infinitive turns the verb into a noun. Using Tijdens het followed by this noun form is a very natural and concise way in Dutch to say "While doing [something]", and native speakers often prefer it over building a full subordinate clause.

Why is the word order "heb ik" rather than "ik heb" in the second half?