I think you mean Jeremy Cross’ first monitor, as Webb (and in a practical sense, Pritchard) monitors were before that.
For additional history, see
http://www.themasonictrowel.com/Articles/Symbolism/general_files/past_master_jewel.htm
This magnificent jewel was presented on April 12, 1831, to Worshipful Master William Cuscaden by Benevolent Lodge No. 142, New York. It is made of gold, silver and composite metal, with inlaid rhinestones and an amethyst, and with what may be a ruby at the top. Brother Cuscaden was first seen on...
nymasons.org
Not all jurisdictions mandate a form of PM jewel.
PM jewels within jurisdictions vary.
https://masonicmedals.net/product-category/medals-jewels/past-masters-jewels-th453-th455/
Brother Cook:
Well, yes, I did mean "Jeremy Cross' first monitor."
I wrote, "... the first monitor by Jeremy Cross in 1819." At the time I wrote it, I didn't realize that it might be misread to mean that the Cross monitor was the first monitor ever. It wasn't.
But, getting back to the simple design of the Past Master's jewel, it did appear in "the first monitor by Jeremy Cross in 1819." Certainly, there were earlier monitors by Webb and Preston, but, to my knowledge, they did not show or describe a Past Master's jewel.
What I am trying to determine is, where did the Past Master's jewel come from? It may be impossible to know who first went to a silversmith and had one made. But, when was the first time that anyone published either an image or a written description of the Past Master's jewel.
I have found a description of the compasses on a "circle of 90 degrees" in the 14th Degree of the Francken MS., and a similar description of a "crownd Compas, the points extended to a Circle of 60 degrees..." in the 18th Degree of the Francken MS, which dates those descriptions to 1783. Granted, they are not Past Master's jewels, but they do consist of compasses opened on a "circle" of either 60 or 90 degrees.
Also, there is a Past Master's jewel, made of coin silver, and engraved with the date "1775," when it was presented by Dona Lodge No. 169 to "Arch. Cunningham, their P. Master." (I don't know where Dona Lodge No. 169 was. But, this jewel sold at auction in 2010 for $800, and pictures of it are shown on the Phoenix Masonry website.
My research to date shows that the original Past Master's jewel was compasses opened on a graduated segment of a circle, with a radiant sun-face in the center. About the time of the Union of 1813, the U.G.L.E. switched to the 47th Problem of Euclid on a square silver plate, suspended from a Master's square.