SDS question


Hello friends,
I was checking my turntable speed today using my KAB speed strobe and found that my table was running quite slow. I had the VPI SDS calibrated at 59.85hz and I thought I had the speed perfect. Today, I needed to adjust it to 60.03hz to get it dead accurate again.
What might cause such a big change to have to be made? I was wondering if it might be the weather (it has turned cold recently here in Chicago)?
Any thoughts would be appreciated.
Thanks.
tfkaudio
are you plugging the sds into the wall or a power conditioner? House power can vary +/- 10 volts at times. I realize the sds is suppose to handle that but I find using my PS audio 300 power plant eliminates this prolem
Its been a while since I was up to date on TT technology. What kind of motor is used? A synchronous motor, common decades ago, would assure that the rpm was exact ("dead nuts" is the technical term). Bearing lubrication, temperature or phase of the moon would have no effect. Only a change in line frequency would affect speed.
Start with the lube and proceed to the belt. I think keeping the bearing lubed may be the most overlooked "tweak" or maintenance procedure. Throwing a few drops of factory-approved oil in the bearing made my near-new Technics SL12x0 spin much nicer and a little quieter.

Belt wear and slippage is a continuous process and usually doesn't get addressed until it's obviously audible. By then it makes the turntable sound like it's seriously broken. But one would think intuitively that a belt could wear and slip the equivalent of .18Hz over time, and one wouldn't notice unless strobing it.
Just following up on Starcons' comments, I was at 60.54 before hooking up my PS Audio PPP. Now the SDS is at 60.00 and my turntable sound is noticeably improved.
OK...I forgot belt slipage. I am a DD guy where the speed of the platter is the same as the motor, and the motor is exact. I really don't think that there should be any belt slipage...you probably need a new belt.