A template is to be located on a pipe but a center finder is not available what else can be accurately mark the centerline?

If a center finder is not available, you can use a method called "scribing." First, measure the diameter of the pipe and divide it by two to find the radius. Then, use a straight edge or a ruler to draw a line across the pipe at the measured radius on both sides, creating two intersecting points. Finally, connect these points to accurately mark the centerline of the pipe.