Need script on speed

I want to make a script that adds speed depending on how often a key is pressed. Like, press W first time and at the second press of W, calculate how long it took for the 2nd press to happen and depending on that, make up a speed. Let’s set the definition of some notations: P1 = first press of W key, P2 = second press, P3 = third press, and so on.

This is a pic i've uploaded, to help:https://ibb.co/bz3WF8

Hope it’s clear till now, so next part: I want the script to calculate the arithmetic mean of thelast 3 speeds, so for example: P1->P2= 2 sec so 20MPH speed, like in the diagram above,P2->P3 =1 sec so 40 MPH and P3->P4= 0.5 sec so 80MPH,mathematically and simplified , it would look like this (20+40+80)/3=46.6MPH. Now let’s call the arithmetic mean of the last 3 speeds an “instance”(like a snapshot that immortalizes some information, so the value of the first instance is the result of the arithmetic mean of the last 3 speeds, so 46.6 MPH, so the vehicle that I drive will move with this speed until a new “instance” aka new speed will appear, the arithmetic mean will done again (the new 3 speeds) and so on. I've explianed in the pic below what I've said in the paragraph above and more.

Another pic: https://ibb.co/jREXNo

Also, I would need a restriction on how often the key W can be pressed, like cant be pressed more than 0.1 secs and need this rule to apply to all calculations, like in ever P1 P2 P3 and so on that appears, each will suffer this limitation. Thank you!