I want to purchase a straight edge which I can use to measure the flatness of heads & blocks and other such nifty things. My question is, what is considered a good tolerance for a straight edge? To make this a little easier, if I wanted to buy a 24" straight edge, how much should I expect it should be straight to across the entire length?
To confine answers, I'm not looking for what you think it should be, but rather what is standard for regular machining practices. References would be helpful.