At a recent checkup, I was shocked: Even though I was eating foods rich in saturated fat and a seemingly more indulgent diet, my total cholesterol was down 10 points, my bad LDL cholesterol was stellar, and my good HDL was the highest it's ever been.
As the frequency of the signal to be measured increases to approach the frequency of the source frequency, measurement error increases. To improve the accuracy of the frequency measurement for higher unknown frequency, we can use this second measurement method, count number of pulses in known time.
The point is, frequency is a measure of how much of one thing for every unit of another thing. It is often how much per unit time but time is not an essential ingredient. Frequency is a MEASURED property. Probability is a mathematical property describing the likelihood of an event.