>...an oval substrate with a minor axis of 2.320, and a major >axis of 3.130. >...locate the two foci of this piece? Bill, For an ellipses with minor axis equal to 2b and major axis equal to 2a, the distance from the center to either foci is (a^2 - b^2)^0.5 In this case, ahh, wait, the calculator is around here somewhere, 1.0505 Anthony