[TenTec] Power indicators??

[P C A]

Hi Folks, I wanted to check the calibration of the Power Meter and the SWR  indications on my TT 238B Tuner. Actually the reading were well within acceptable limits as per the procedure in the operators manual.However, I noticed a big dependency in the power indicators on my Oll.  With the pwr set at 25w a on the display the analog meter read 46w and the 238b read 20w, the bird showed 18w.  At 50 w on the display, the analog meter showed 78w, the 238B showed 40w and the bird showed 42w. At 100w on the display the analog meter was pegged, the 238B showed 99w and the bird showed 100. Anyone know any calibration procedures for the Orion? Nothing in the manual.Also, what size Torks driver do I need for the cabinet screws? Tnx Andy