Learn Turkish: O kritik göstergeye dikkat etmediği sürece gemi ilerlemez. - As long as he does not pay attention to that critical gauge, the ship does not advance.

You add the negative suffix -me or -ma directly to the verb stem, before the -dik suffix. Here, dikkat et (pay attention) becomes dikkat etme. Then you add -diği (the -dik suffix softened, plus the 3rd person possessive -i) followed by sürece. Together, dikkat etmediği sürece means "as long as he/she does not pay attention".

How do we know it is "he" who does not pay attention, but "the ship" that does not advance?

The sentence has two different subjects. The main subject is gemi (the ship), which acts on the main verb ilerlemez. The subject of the first action is marked by the possessive suffix -i on etmediği. This suffix tells us a third party (he, she, or it) is the one ignoring the gauge.

Why does gösterge (gauge/indicator) take the -(y)e suffix here?

The verb phrase dikkat etmek (to pay attention) always requires the dative case because you pay attention "to" something in Turkish. Therefore, gösterge gets the dative suffix -ye, becoming göstergeye (to the gauge).

Why use the aorist tense ilerlemez instead of the present continuous ilerlemiyor?