How can I tell if the mower blade is flat?

[Jorabi]

A friend of mine is sharpening the blade from my Craftsman walk-behind. I asked him to check the alignment also, and he looked at me as if I had two heads. He said, "Do you mean the balance? Because I check the balance by rotating it on a peg when done and take off more from one side if I have to". I said no, I mean to check if the blade is flat and level, so that it cuts evenly. I could not make him understand what I meant, but maybe it's because I am worrying about something that doesn't matter. Doesn't a bent blade cause a poor cut?

 

[StarTech]

Yes it does. Some that come in here actually plow up the ground under the deck. Basically the blade have to be mounted to check this. Even if the blade are straight a spindle shaft or spindle mount could be bent.

And sometime it is only the thickness of a blade but some grasses can really show it.