Installing cartr.:slide it all the way to front?

Dougdeacon, my rega300 installed on an AlexMkIII has the following geometry. Pivot to spindle at 222mm and stylus nulls are at 64mm and 120mm, which seems to be close to the figures that you have mentioned. Cartridge is a BPS. I thought that those figures might be of assistance here. I used a protractor that was published in HiFi World.
Salut, Bob P.

Mario,
That's the spirit! I first did this just like you're planning to do, by trial and error. I tried to set up my OL Silver/Shelter 901 at the OL-specified 223mm using a TTB protractor. No dice. The stylus couldn't be aligned at both points. I sat down and thought through the geometry, slid my armboard in a couple of mm and, bingo! Problem solved.

It was only later that I got my head around the theory (a little) by talking with real mathematicians on VA and reading some of the papers there. If you want real math, go there and search for posts by John Elison.

Again, anyone can choose Rega's Stephenson geometry and have no problems at 222-223mm. I just like Baerwald's theory (lowest total distortion) better and appreciate the greater accuracy the TTB's mirror makes possible. Frank Schroeder uses a DIY protractor he printed on a piece of card, so if you prefer that you're in the best possible company. I just like the mirror.

P.S. Whatever protractor you use, don't forget to disengage antiskating!

Bob,
Thanks for sharing that info. Null points at 64/120 are pretty similar to 66/120.9. I think the key is that you're at 222mm whereas my Rega style arm specifed 223mm, which definitely didn't work.

Another variable is the stylus-mounting screws dimension. The farther the stylus is ahead of the plane of the mounting screws, the farther the arm can be from the spindle. I don't know your BPS but ZYX's and Shelters are both about 7.5mm, which is on the short end of typical. Some cartridges run as long as 9mm, which would probably make adjusting the arm unnecessary.

inpepinnovations@aol.com, here is the data on Rega Arms given their standard mounting distance at vinylengine.

http://www.vinylengine.com/tonearm_database.php?make=Rega&sort=manufacturer&ascdesc=ASC&type=1&pass=null&Search=Search

Dougdeacon, the BPS stylus to mounting screw distance is 8.2mm.
Bob P.

Bob,

That extra mm explains why you can reach null points similar to Baerwald's while shorter cartridges can't quite make it before hitting the front of the slots. (I assume you're pretty close to the front.)

Thanks for some interesting info,
Doug