Why Do 12" Tonearms Cost So Much More Than 9"?

Forgot to say to Elliot, that Blackbird tonearm is "controversial" to say the least.  You might have asked here about it before taking the leap.  I think Chakster has some info.  I hope you'll be happy with it.

mijostyn

Schroder LT.
The Reed 5T is another example. These arms stay tangent to the record, do not skate and totally avoid the problem of very high horizontal mass which plagues the vast majority of designs.

Any pivoted arm is subject to skate, a force that is the result of both the pickup arm's pivot and its offset, if any. None of this is a mystery and an arm's skating force can be measured.

There have been a variety of "pantograph" type arms over the years, the infamous Garrard Zero100 being one especially unpleasant example. I don't have any experience with any of the newer tangential tracking efforts, which include the Nasotec Swing headshell and Klaudio arm. But in the past, a prime problem with these types of devices has been friction, so the cure was worth than the disease.

It's quite interesting on error in relation to arm length.

Simple math states that from a pivot point of A to a fixed point of B that the greater the length between A and B is then the greater the measured error will be at point B from a change at point A.

For example we install positioning lasers about 12 to 18 feet from a target so the laser is point A the target is point B.
At 12 feet for point B if I have an error of say 1/4" this grows to say 3/8" at 18 ft target distance or new point B.

However it really does not seem to be borne out in practice with tonearms.
Most interesting indeed.

Cleeds makes a good point that I’d never considered. Any of these fancy pivoted tone arms that incorporate a device to keep the stylus tangent to the groove at all points across the surface of the LP would nevertheless generate a skating force. In this case, the skating force would result from the constant fact that there is a head shell offset angle which is changing all throughout play.

Uberwaltz, The analogy you gave for why measuring errors are magnified in proportion to distance is exactly what I have in mind as a reason why errors made in mounting 12-inch tonearms might be more consequential than errors made in mounting 9-inch tonearms (and also mounting and aligning cartridges on either type).  But why do you conclude that this proposition "does not seem to be borne out in practice with tonearms"?