I need to modify an android app

My english is quite bad.
So, I'll just paste the e-mail that I sent to a developer.

Hello!
I'm sending this mail because I thought about an idea that perhaps you may be able to achieve!
The idea came using your 'Audio frecuency counter' and my new bike.
After adjusting the input audio parameters, y managed the app to count and calculate the frecuency of the vague sound that a piece of adhesive tape situated in the air valve of the wheel makes when this wheel is spinning. Of course the sound is coming in from a cheap headset microphone located close to the tape, and you can easily connect the phone to that cable.
And as you sure know, this way you can use the frequency and the wheel's radius to calculate the linear velocity of the bike. And it results in an alternative to gps speedometers!
I don't know anything about programming apps. So I have to use this system multiplying in my head the frecuency by the conversion factor corresponding to my wheel's dimensions.
My english is quite bad, but hopefully you'll understand.
Let me know what you think about this!
Greetings!
Francisco.

So.. Can you people make this modification to the app and share it with me?? Of course it is a non-profit thing.

Really!?
I thought it was easier than that..
Thank you!