Electricians often need to locate the center of a bend that they have made, or the center of a bend that needs to be matched or aligned with a new bend.  A small torpedo level or straight edge is laid along the inside of the bend so that one end extends past the top of the bend.  A line is then drawn on the conduit along the edge of the level or straight edge.  The level or straight edge is then placed along the other side of the bend, similar to the placement for the first line.  A second line is then drawn on the conduit along the edge of the level or straight edge. If the bend in the conduit is small, the two lines should cross.  This point is the center of the bend.  As the angle of the bend increases, or the centerline radius of the conduit increases, the two lines may not actually cross.  The electrician can usually measure the distance between the lines to mark the center of the bend.