Doesn't look like it has ever been used, part #PC-100
From their website:
Adjustable on-head valve spring pressure tester for various shaft style and stud mount roller rocker systems. It features a 0-600lb gauge. Comes with adjustable shim kit which enables adjustment to within .050 of rocker arm pivot length. Includes set-up and adjustment guide.
Sells new for $230
Midwest Speed Shop
573-694-9847 cell call/text