Hey Michael R 1974!
It got sunny just long enough late afternoon for me to take some high flare and low flare shots. I added some sensitometry to the rolls for a baseline curve.
Methodology: Sekonic test target with a black patch, white patch and 7 gray patches. The gray patches are centered on 18% (yes really). Total range is 1.4 log units, the gray patches are closely spaced. 100 TMAX 35mm in an ESII with 50 f/1.4 SMCT at f/5.6 for 1/125 sun facing camera (high flare), then another shot with sun facing target at f/16 for 1/250 (low flare).
Results: Low flare so low it is not measurable. High flare is 0.26. Classic taper of flare curve to nominal curve.
Another test using M2 with 50mm Summicron but with a UV filter that has significant cleaning marks... Difficult to measure because image was smaller on negative... Some abrasion marks interfered with high flare shot readings... Exposure error forced me to do some interpolation of my readings... Results of that test: Low flare 0.28 High flare 0.74. That test is not worth showing, but I think it helps validate the methodology.