I made an investment in a Quick Stick: http://www.bhphotovideo.com/bh1.sph/FrameW...SID=F222E9DD670 . The thing is made by Visual Departures ( http://www.visualdepartures.com ). Somebody gave me a pair of el cheapo tape measures and I marked the backs with the necessary factors (in 1/3-stop increments). The final product is quite compact and easy to use, and I have the Quick Stick as a backup in case I ever need to make more tape measures.