How do you tell if head is warped?

To determine if a head is warped, you can perform a visual inspection for any noticeable irregularities or gaps when the head is placed on a flat surface. A straightedge or ruler can be used to check for unevenness by measuring the distance between the head surface and the straightedge at various points. Additionally, using a feeler gauge can help detect small variations. If significant warping is detected, it may require resurfacing or replacement.