Question

what do you mean by flatness and shrilness ?

Answer 1

shrillness also known as pitch as frequency
flatness also called as amplitude it start from it mean position

Answer 2

In GD&T flatness tolerance defines a zone between two parallel planes within which a surface must lie. Sinceflatness is applied to an individual surface, this tolerance does not need to be related to a datum.
sharp, like the squeak of the mouse in your cupboard or the sound of your “eek” when you hear it. Closer to a shriek than a trill, a shrill tone is one that might make you cover your ears, usually because the tone is so high and sharp.

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