While mapping an argument in standard argument form can be a good way to figure out and formulate a thesis, identifying arguments by other writers is also important.
As for mistaking a fact for an argument, keep this important distinction in mind: An argument must be arguable.
It isn't scientific there is a more scientific way in Oculus calibration or your optometrist can give you the exact measurement and you can try that.
He did so to refrain his carnal desires.