I believe input capture (ICP) is pin 8 on the Arduino Uno pinout. If you're measuring a fairly slow signal, under a few kHz (or 10000 RPM motor), pin 8 with a library like FreqMeasure probably makes more sense. For full disclosure, I'm the author of FreqMeasure....
But for higher frequency, you probably do need pin 5, the external clock input for timer1, and perhaps my FreqCount library?
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