These precision rulers have patented marking holes at each measurement where you can insert a thin pencil, pen or stylus and mark your measurement with accuracy.  

They come in a variety of sizes to suit various book and box making applications: 

3" pocket sized. $10.95 
12" marking. $21.95 
12" centering. $29.95 
18" marking. $31.95 
3" T rule. $14.95 
12" T rule. $36.95 
18" T rule. $46.95