I found my sweet spot for bicycle size by trail and error. Over the years it has slowly changed so I now keep detailed specs on what feels comfortable for me. If you have been riding regularly you should be able to find your sweet spot pretty easy. Once found take those measurements and keep them close.
Note that at 70 years my bikes are not set up anything like they were 50 years ago... Ha
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No matter where you're at... There you are... Δf:=f(1/2)-f(-1/2)