The problem I have is the pic has to act quickly, the engine revs very quickly, and if it spends 1 second counting pulses, it will probably be over-revving by then.
Of course, at 1 kph, the pulse period is 2.2 seconds, and that's how often you can update the display. But at 1kph, you don't need a faster refresh.
Hi, folks ...

Problem is Here, not a display problem ...

You need quasi " real-time updated speed " ( Cf Post # 2 ) ...

Alain

PS, Don't tell " Davewanna" , BUT

"Dave would have liked to" ... Humour !