Larry,
As one who has been striving to get one of the "piezo" "gizmo"s working, let me belatedly announce that we finally have a working system... so to speak. I found that the piezo sensor we had that clamps onto the heavy fuel lines used on these vintage MBZs, I found our clamp sensor was apparently defective. So two new piezo clamps [ 6 & 5 mm] did the trick. We are using a Kent Moore "Tach-N-Time" meter I purchased on Ebay for ~$200. Let me point out that the standard inductive strobe light I initially used was NOT sensative enough but my Indy friend "Karl" the mad Hungarian has a "Snap-On" light that works with the meter every time now. Another part of this "show-n-tell" is that after using our timing meter/light on numerous 70(s) and 80(s) MBz diesels [ several at our last S.F. EastBay GTG in July]... after this considerable experience with our working meter/light, I can report that most cars have been found retarded 4 to 10 degrees or set at from 14 to 20 degrees BTDC. My Son's '80 300D IP was off by 11 degrees and once reset ~26 deg. BTDC the car's fuel mileage has improved about 15 %.

Let me say IMHO a practical accuracy for timing for us at present is ~ +/- 1 degree largely due to the limitations of being forced to make the adjustments "statically". Now IF only we could figure out a way to make the timing adjustments "dynamically" [ aka with the engine running ]!?
I'm thinking that we might try fabricating extra long HP fuel lines that would be used temporarily for IP timing adjustments. Such fuel lines would loop much higher and thus be flexible enough to allow the IP to be turned/ adjusted while the engine is running. "Yellit" and I have also talked extensively another yet to be successfully invented tool... some kind of attachable lever/bar/handle that would extend up and out of the engine well to increase the ease and accuracy of your IP adjustments! "Yellit" [Kevin] and I would appreciate any thoughts/ideas that you might have on either of the above described yet-2-B invented tools needed to add the ability of dynamic timing adjustments to go with our now functioning meter and timing strobe light!

Even with such tools, I think +/- 0.5 degrees would be the absolute best one should expect... and probably 1 degree is more practicable... so I truly hope Barry is correct that once we get this close to what he believes is the ultimate "sweet spot IP timing setting"... I hope his Glow Plug MiliVolt Method can then take over and together with our ideas for flexible test/adjustment fuel line and attachable lever/handle... then we will have a workable way to "tweak" these IPs/Engines probably somewhere near the 26 deg. BTDC mark!
Regards,