A friend and member of my local HiFi Club has a substantial tube collection with items spanning two generations of collecting.
A Calibrated Tube Tester is a important part of this enthusiasts activities.
It is great to be introduced to same era Tubes with usage life beyond factory spec' and almost perfectly matched in each half of the Valve across Valve Pairs or Quads.
It is only through being introduced to same Brand Valve as per the above and then compared to same Brand valves with a reduction in usage life and a wider range in the readings across each half of the Valve, does one discover the real attraction of very accurately match Valves.
It is something quite special to experience a near perfect match array of Tubes. Having access to the Tube Tester for periodical readings helps greatly with assuring the optimised experience of Valves is being maintained. These Types are usually the Sunday best and lesser quality matches are identified do the daily grind/glow.