Ok, I think I know where the problem is. Look at the pictures of the ParaCorr parts on TeleVue's web site. They have two different tunable tops with different height 1.25 to 2" adpaters. The old style is 0.16 in thick. The new style is much thicker (I don't have one to measure but it looks to be about 3X the old adapter). In the equation in my post above, the TeleVue ParaCorr setting do work out for all of the 1.24" eyepieces if the adpter thickness is set to 0.37 inch. I did check the above posted equation in a spreadsheet for all of the eyepieces in the ParaCorr Setting Chart (the chart is not correct for 1.25 eps using the old adpter thickness, decrease the setting by 2 is close to correct). Also note that TeleVue states that "set path length from Paracorr flange surface to CCD surface to 55mm ±4mm for best results". ±4mm = ±0.157in, whereas a chenge from one setting to the next = 0.12in. This ± 1.3 settings, so there appears to be a fairly wide tolerance to get the correct setting. Would you like a copy of my speadsheet? walt