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.
If you are making one in 4x5 then consider sourcing .1 .3, .6, and .9 ND fiters, slice them, tape them ( use clearest tape you can find) to make different stacks to go from .1 to 2.7.
Rosco makes inexpensive .3, .6 and .9; I don;t know where other than Wratten for .1. The trick is to make sure that the film HD performance is straight line as you can imagine. I think I heard that Stouffer uses a stash of tech pan and careful exposure and development.