Difference between using different ardunios

I have to construct an ECG for my school project and i am facing some problems. While searching the internet i found a website to hook up and construct the ECG(AD8232 Heart Rate Monitor Hookup Guide - learn.sparkfun.com). The program works if i follow the steps completely, like even the arduino type(pro mini) must be the same. I do not understand why a different arduino would show a different ecg signal. Can someone explain if i use a different arduino should the processing code also change? If yes how? Thank you for your reply in advance.

The reasons for using different Arduino's are varied.

The "standard" model is an Uno.

The reasons you would upsize to a Mega is if you needed more I/O's or memory.

The reasons you would downsize to a Nano or Pro Mini is if you have physical size limitations to your project.

Stick with the Uno if it meets your requirements - you can't go wrong.

Edit: As the next poster pointed out, I did not address the issue of code changes. I believe the only code changes that would be required would be pin assignment, where the different models do not use the same pin numbers - particularly when using the Mega.

Can you tell us which other Arduinos you have tried this with? And how the ECGs are different?

aisc:
The reasons for using different Arduino’s are varied.

The “standard” model is an Uno.

The reasons you would upsize to a Mega is if you needed more I/O’s or memory.

The reasons you would downsize to a Nano or Pro Mini is if you have physical size limitations to your project.

Stick with the Uno if it meets your requirements - you can’t go wrong.

I think your missing the point of the question. Why are the ECGs different with different models?