Datum II & IIs
The Datum I was manufactured by Syrinx and up to that point had threaded posts and nuts to mount.
Logic aquired Syrinx and made in house the Datum II & IIs with the three point mounting collar. They mounted both Datum’s on their DM101 and Logic Tempo turntables.
Mounting hole 30.5mm
Effective length 228mm
Pivot to spindle 210.7mm
Overhang 17.3mm
Azimuth is adjustable by two bolts.
You are correct the counter balance is very up close to the pivot due to the tungston counter weight.
All of the Syrinx arms…LE1, up to the Datum I had the same measurements and these were carried over to the Logic produced Datum II & IIs
One thing to note is that when Logic folded the companies stock was bought by Manticore Systems Engineering. Their well liked Mantra turntable was a leading model in the UK. The later Datum IIs arms were modified to their new specs under the MSE logo which appears on the arm pivot. Superior bearings and improved external finishing also cured the anodising effect of UV in earlier models.
A Datum IIs with the silver wire was considered better than the Linn Ittok LV3 Mk2 and considerably less expensive. The Datum I, Syrinx PU2 and PU3 models were claimed by some to be ‘’Ittok Killers’’ within their individual timeframes.
Search the ‘’Vinyl Engine’’ archives further to confirm this information if you wish. l own a few Syrinx arms so l am sure l have given you the correct info.