Heater Intake Grille

My first attempt to compare the curvatures was to lay a straight-edge with its centre of balance over the last square hole in the grill at one end, then measure the distance between the end of the grill and the straight-edge at the other. Several milli-metres less, difficult to photograph with a rule, but you can see the difference between Vee's problem grille at the top, Bee's good grill in the middle, and Vee's original grill at the bottom.

Then as I was using a spirit-level I hit on the idea of comparing the bubble positions when positioned over the end square hole on each grille. Vee's here with the bubbles barely off-centre:

And Bee's here with the bubbles right at the ends of the glass tube:

Then I had the idea of going back to method 1 but using drill shanks to gauge the gap rather than measure directly. With the straight-edge pressed down over the last square hole one end, I inserted drills between the straight-edge and the last bar at the other end. With Bee a 15/16" drill shank was fractionally too big and a 7/16" too small so about 11.4mm, whereas on Vee I could only get a 5.5mm drill shank in, so half the curvature.