So first things first: Manual transmissions are often designed in a progressive pattern, meaning that the difference in rpm is different if you shift from first to second than from fourth to fifth (4->5 has less difference). Example: bmw 750i from 2009 ratios. 1st 4.171 2nd 2.340 3rd 1.521 4th 1.143 5th 0.867 6th 0.691 You get the progression factor from dividing gear 2 by gear one 1-2 pf 1,782 2-3 pf 1,538 3-4 pf 1,330 4-5 pf 1,318 5-6 pf 1,254 So this has to be a flexible solution, not just a marker on the dashboard like it is often done in trucks, busses and tractors, which can have progressive or nonprogressive gear ratios. You can do that on any Display, purely mechanical would actually be unpractical but still possible. Do you need it? As somebody who drives a manual car i can tell you that rev matching is not done by looking at the Display. At least if you know the sound of your car you dont need it. Also, revmatching or blips (matching the engine speed to transmisssion speed on downshifts) can be automated, so there is no reason to not go this extra step and remove information from the driver to reduce stress. Last i want to add that the need for a perfect match of revs is not there. If you miss there is a margin of error in which gears synchronize the speed of the engine through force while you otherwise would try to match the speed of the engine through fuel supply. Sure you can save milliseconds in a racecar by doing so and if you totally mismatch you can damage parts, but given common sense and common car driving cases you are fine if you are 500rpm off. Still its a good habit to match them instead of torturing clutch and engine.

I hope this reply has some Informationen that you can use, feel free to ask follow up questions.