derpyhero

I've got a standard electrolysis IA, my dependent variable is obviously the deposit of the ion on the other electrode, but my independent variable is surface area. I've had some troubles with coming up with a way to test this, but I've concluded the the best way would be to cover up some parts of the electrode with waterproof tape. What uncertainties may be present? How could a certain amount of waterproof tape placed onto the electrode to test surface disrupt the electrolysis?