Excel spreadsheet formulas to calculate the frequency of a waveform given a set of data points

I have a spreadsheet (see file) that has output from a pressure and flow sensor showing 5,000 readings in 1 second. I need to have a formula that will calculate the frequency of the pressure waveform. In the example I have counted 18.8 as an estimate. My problem is that I have over 100+ samples and I need to automate the process. I desire a Freelancer math / Excel expert to write a formula to calculate the frequency? To calculate the frequency one should count the number of cycles in a period. Frequency = cycles / seconds. If you could devise a series of IF statements to count the number of true low points in the data, then minus 1 which will yield the number of cycles. You can then isolate the time that the first and last low point, use a MIN/MAX subtotal to find the time the first lowest point and last lowest point occurred which will yield the period of time it took for the cycles. (Frequency = cycles / seconds) One can then calculate the frequency if we know the # of cycles and the time it took to complete. My challenge is to devise the logic of IF statements (or other counting schema) to identify if the points are going up or down and if they are the lowest point. The attached file shows the pressure wave on the bottom. You can count the number of cycles and see that it is 18 plus a portion. This is the answer that the excel sheet should return.