There is no notch on the T2. In our 80+ GB and multiple bar FeO2 soil, 99 sensitivity is useless as is very low disc. Disc at 10 on a F75 knocks out almost all iron. Iron on a T2 discs out at 40.
Here is a chart:
Model - Teknetics T2/Software version 6.5 (from 6.0 onwards version numbers make no difference in depth according to First Texas Products)
Coin Used - U.S. Quarter - Cupronickel
Coil - 5" DD
Sensitivity - 60
Tone Selection - 4
Discrimination Levels
0 - 9" depth reading (extremely noisy due to EMI & machines internal circuitry noise)
10 - 7" depth reading (approx 50% less noise than 0 disc setting)
21 - 6 1/2" depth reading (quiet)
30 - 6" depth reading (quiet)
40 - 6" depth reading (quiet)
49 - 5 1/2" depth reading (quiet)
50 - 9" depth reading (this is where another huge increase in Gain occurs, besides the zero setting. Same noise level as 0 disc setting)
60 - 9" depth reading (approx 50% less noise than 50 disc setting)
70 - 8 1/2" depth reading (quiet)
80 - 8" depth reading (quiet)
Observation - the Gain does not seem to follow a straight linear output as disc is increased. Notice that from 0-49 disc there is a 3 1/2" range in detection depth. From 50-80 disc there is a 1" range.
0r
If you remove the disc 0-9 results from above, there is a 1 1/2" depth range between disc 10-49 and a 1" depth range between disc 50-80.
The large gain increase at 50 and the 10-49 disc range has serious implications on how a user sets the discrimination. Below are object disc ranges on T2:
Notice the depth is the same at 50 (into foil range) as it is at 0 and disc at 10 reduces depth 2". Reminder: this is the small 5 inch coil. If I had it to do over, when I first got my T2, I should have set disc between 50 and 60 and learned what the good targets sounded like before using less disc. There is a difference in the sound after using it a while. If you get a short beep and turn 90 degrees and get a slightly longer one, it is not a round object. Good luck. I think you have a very competent detector. Switching from one good one to another takes a while to comprehend what the other is saying, especially after using the first good one for as long as you have.