Make a note in the logbooks and placard the correct (indicated) RPM
When I was a student PPL at solo stage, I flew one of the club's PA28s solo - the first time I'd ever flown this particular aircraft. I was just doing some circuits, but something didn't seem right. I remembered my instructors words - if something doesn't seem right, the chances are something isn't right, check and re-check everything.
So I re-checked. I had no flaps deployed. The RPM was exactly what it would normally be at this stage. I was flying level. But my speed was much too high. That was when I noticed the sticky label under the tack - "Tach over-reads by 200rpm". D'oh! It was actually underneath a bit of a ridge on the instrument panel, so that anyone taller than about 5'8" wouldn't be able to see it from the "normal" seating position. Everything was fine once I'd taken the error into account... fortunately, I hadn't been doing any dives which would have oversped the engine
If you're going to placard something, make sure the placard is where people can see it!
FFF
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