I have a question that Ive been meaning to ask for a while now. Is using a circle guide considered cheating?

Basically what they are, are tops/lids from things like fruit drinks and one from a paper tube you keep used to keep your artwork in back in high school.

Then from there, I place them over the head of the picture im working on to double check if my circle, the head is round enough or not.

So yah is it cheating or not. what do you think?.