Progress report!
Here it is 3 weeks after the great advice from all of you and yesterday cannonfodder came over with his scace and we spent a couple of hours pulling shots of SM's Ophiolite that I roasted and the Intelligensia Black Cat SO. I really apprecitate the time Dave took from his busy schedule to share his expertise personally.
Over the past couple of weeks, I have reduced the brew pressure to 9 bar and installed the group temperature probe from Chris's coffee. Yesterday, Dave and I determined the temperature characteristics of my Andreja Premium and that is going to help a lot. Dave pointed out that I wasn't quite level in my tamping and that I needed more precision in my scale which only measures to the nearest gram. We found that I was probably overextracting and getting bitter flavors. My time was OK, but I was getting a little too much volume.
Anyway - thank you all!
It's really nice to have such a bunch of experts available to help a newby - I feel like you all jump started me toward good consistent espresso!
Mac

Since you were (lucky enought to be able) to use a SCACE along with your group thermometer on the Andreja I was wondering if you could share some of the temperature differentials during a shot between the two readings?

Thanks

OK, I'll try to pass on what I learned. We didn't record anything and it happens very fast. I discovered that there are significant differences in the initial difference between the group head and the scace depending on how long since the last shot. We were doing flush and go. I learned to flush until the group head is about 2 degrees above desired brew temp and that the brew head and the PF temperature are very close (within 1/2 degree) in the last part of the shot. The flush temperature difference decreases if it hasn't been very long since the last shot and increases if it has been a long time. I learned to watch the group head temp at the end of the shot to see where I ended up. It all happened really fast and perhaps Dave can correct me where I'm wrong.
Mac

EDIT: As I reread this it sounds like I didn't learn anything from Dave or was ungrateful. I was neither! I'm guessing the uncertainty in the post reflects the fact that I'm still in awe of the process of making good espresso. I never imagined that there could be so many interrelated variables in general, and specifically that the process of flushing a HX machine would be less than simple once temperature measurements could be brought into play! So with good guidance from the forum and Dave, I'm trying to become one with the machine and my shots, less than perfect as they may be, are good. I'm enjoying the journey. Thank you all! Mac