I think in Tube DIY world must know Tube Tracer that can trace tube's characteristic curves.
And now eTracer from Essues is latest smart vacuum tube tracer/tester.
You can access their website and study how it work,
https://www.essues.com/etracer/
or find many of tube amp designers who using it and post on their blogs.
Connect to computer via USB cable and fully control with program, easily change parameters
like filament voltage/current, plate voltage/current, load line, etc.
1) match pair or match tube's sections with their characteristic curves not life time!
2) get accurate values to use in real circuit not common values from datasheet provided!
3) best for me is can plot triode curve from pentode tube that cannot find from any source!
To be continue...