Why does the current cz-3d not come close in depth...

Why does the current cz-3d not come close in depth to the Los Banos 1021 s/n detectors made almost 20 years ago?

Those 1021 units seem to average around 12" depth in Tom's dirt when he calibrates them.

The couple times I've seen newer units Tom tuned it was around 9" depth.

So what is FT doing differently now? Why aren't current cz-3ds averaging around that 12" mark?

I could make an uneducated guess, but I really don't know.

So could Tom or anyone else who does know explain?

Do a search on this forum, there is a lot of info on this particular subject.

( Quality Control) comes to mind and not all of them as have used both and either were deep seekers) seems like many variables to tuning and if not Tom usually brings them up to par.
Using ever model CZ ever made(some several times) I feel right out of the box and years later CZ6A's are my favorite and go as deep as any coil for coil with rare exceptions and offer weather resistant features.( Guess thats why some have brought out of sight amounts lately)
Just a laymans view who has used them for 20 years or so and Tom can add the technical aspects...