Rob's panel gauge has a 20" beam.  The figured maple head is held tight with a tapered and trapped wedge.  For precise marking one end uses a 5/8 diameter cutting wheel that can be rotated when dull and easily face honed when needed.  The other end is designed to hold a pen or pencil for close measuring.  The gauge is soaked for days in Tung oil for a deep penetrating finish.  Purple Heart beam, figured Eastern Maple head, tropical hardwood wedge.