Learn Turkish: Ölçüyü senin söylediğin kadar santimetre azalttım. - I reduced the dimension by as many centimeters as you said.

This uses the structure you are learning in this lesson. We take the verb söylemek (to say), add the -dik suffix (which softens to -diğ), and attach the possessive ending -in to match senin (your). When followed by kadar (as much as / as many as), the whole phrase senin söylediğin kadar means 'the amount that you said' or 'as many as you said'.

Why is the word santimetre singular when the English translation says 'centimeters'?

In Turkish, when a noun is modified by a number or a quantity expression, it stays in its singular form. Because senin söylediğin kadar acts as a specific quantity modifier ('as many as...'), santimetre does not take the plural suffix -ler.

The dictionary says 'to decrease' is azalmak. Why is the verb azalttım here?

Azalmak means 'to decrease' on its own (for example, if a temperature decreased). However, when you actively reduce something else, you need the causative form azaltmak (to make decrease / to reduce). Since you are the one reducing the dimension, you use azalttım (I reduced).

Why does ölçü have the -yü ending to become ölçüyü?