So I've wrestled my benchtop for the last month and I'm finally making progress. I used winding sticks today and everything looks good. However, when I use my No 7 Stanley to check for flat across the width I can see small amounts (1 cm or less) of light coming through. I used my framing square with similar results. I don't own any measuring tool that is 24" long and guaranteed straight. My question is how "flat" do I need the top to achieve a reliable reference surface for planing? I am planning a lot of hand tool work making jewelry boxes, furniture, and toys. I'm frustrated bc my jointer sole measured flat to me ( about .0005) or so with a feeler gauge all around not able to slip under the sole. But I still see surface variation under the measuring tool all along the length of the benchtop measuring across the width. I will admit to being somewhat obsessive about exactness.