I have had a few. Never the calibrated ones. The simplest was the Kodak projection print scale.
The next was a little Geavert (sp) half stop per step without numbers 1" x5", with a pair of pin holes pushed though the neutral grey step.
Then a Stoffer half stop per step 1/2" x 5 or ", each step numbered I think, commonly used in the alt process and screen printing trades, printed with every sheet in the margin.
Most recently a 2.25" square 1/3 stop per step to aid me in calibrating old VC and fixed grade papers and VC dial setting for projecting b& w negs.
I went with this becasue I wanted to calibrate 6x6 and 4x5 enlargers, and wanted to be able to project it from a neg carrier to see if there was a difference from calibrating it when contact printing it.
The prior step wedges were all free, but this one I spent $50 on direct from Stouffer, and consider it money well spent. Ordered over the phone, with excellent customer service and timely shipping.
I use it every time I open a new, or new to me, package of paper. I have even placed it in a slide copier and used it to evaluate the HD curve of meduim format films. On 4x5 I just tape it to the film in the holder and expose to a white wall to get the steps to read off the film after development.
