Help when Eye-Balling Router Bit Height

I don't have any photos to include here as my router table is currently dismantled awaiting a weekend to install it in the right extension wing of my new SawStop.

Many times you know the bit height needed by relative measuring.  That is, you have placed a scrap piece into the project and marked it directly off the project.  This is always more effective than trying to measure "a heavy 1/4 inch" and marking it.  Normally, you sight down the edge of the table to see where the bit will cut in relation to the score line you made on the scrap.

What I do instead that helps greatly is to put a penlight flashlight on the table casting the bit's shadow onto the scrap.  It is very clear, even in daylight, where the top of the bit is located.  If the penlight is small and the bit height quite high, you can get an error due to the predominant incidence angle of light, however the error will be in cutting shy not too heavy.  Generally my 1" diameter penlight gets me dead on first try with the scrap with no squinting.