Flatness on a Per Unit Basis

Jason discusses form controls on a per unit basis using the example of controlling flatness on a large surface in this Question Line Video.
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[@kunwarmahto6889]

Very helpful video sir 🙏

[@asaholey]

How do I apply flatness to just an area? Example 50mm diameter from the center of 100mm round plate

[@Gdandtbasics]

That a great question. We can utilize a datum target area. Which will essentially be a 50mm diameter circle drawn directly on the drawing with hatching inside the circle. The circle size is dimensioned on the drawing with a basic dimension of 50mm. And the flatness callout will point to that area, indicating that the flatness only applies to the hatched area.