Tach. issue....

I have a 1980 corvette and it had a dead tach. I bought a used one off ebay and installed it..It works perfectly, however i noticed something on the old tach after I had put the dash back together. The original tach had a rectangular cutout under where it says rpm on the bottom and the one i put in doesnt have it... For the life of me i cant figure out what that cut out was for and i'm trying to aviod taking the dash apart again. Does anyone know what it was for...(a warning light maybe???)I know I should have compared them side by side but i was anxious to get a working tach in and overlooked it....

Reading from my restoration book it states the following.
Quote"Again almost a complete carryover from 1979, the main instrument faces each had a crossed flag emblem to match those on the body. The tachometer had a choke warning light and the 1980 L82 a matching emblem too. Only this tachometer had a 6000 rpm readline, all others being redilined at 5300 rpm." end quote

Maybe this will help solve the puzzle

thanks for a quick response...