Look at these weird turboprop N1 gauges:
I'm referring to the smaller needle at the top of each PERCENT RPM labelled N1 gauge. What does it display ? I have no idea.
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2$\begingroup$ I don't know anything about that specific aircraft, but just from what I know of gauges in general, it looks like the units digit. So the left hand one is reading 1% and the right hand one is 0%. $\endgroup$– Greg HewgillFeb 17, 2022 at 1:19
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$\begingroup$ @GregHewgill ahh, yeah, if you look very close the left big needle is indeed deflected from the 0 mark a very little bit. Thank you very much, this was the pointer I needed ! :) $\endgroup$– TheEagleFeb 17, 2022 at 1:22
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2 Answers
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It duplicates the percent graduations in the large dial but at a finer resolution, with one percent increments. It's just to make the individual percent graduations easier to discern at a glance without having to squint down at the gauge to judge where the needle's point is relative to the little hash marks, which are in 2 percent increments.
When the big dial moves from 0 to 10%, the small dial makes one full rotation. So when the big dial needle is at 5, or 15, or 25 etc, the small dial will also be at 5 (6 O'clock).
You can watch it in action here at about 1:25.
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If the engine is at 95% RPM, the large needle will point halfway between the "90" and the "100" indication on the outer scale, and the needle on the small dial will point to the "5" mark on that dial.
The smaller dial makes it easier to read an exact RPM, to a precision of about +/- half a percent.
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6$\begingroup$ The smaller dial also makes it easier to judge if the RPM is changing and in which direction. $\endgroup$– jpaFeb 17, 2022 at 10:37