Love the old military relics. !
I experimented A LOT with modes during the first several months I had my 800, comparing targets under the coil, but I always came back to Park 1 for MOST all areas. Park 1 seems to provide the best audio and visual responses especially as targets gets deeper or more difficult in my areas.
That said, Today for the 1st time since I've owned my 800 I had to go single frequency and stay there due to EMI. I was hunting an old yard on a corner and the overhead power lines on both street facing sides was just killing me. I kept noise cancelling and reducing sensitivity and was all the way down to 14-15 AND still struggling. I finally gave up and went for the FREQ button and started slowly cycling through the frequencies. 5kHz, 10khZ and 15kHz were great, 20kHz and 40kHz not so much. I ended up on 15kHz and was able to get the sensitivity back up to 21 without issue.
I'll be watching for your "follow up" post if you make it. I frequently turn up rusty old nails or pieces of nails along with a good target with the 800. The EQ seems to have a skill for it.
Rich
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800 - Deus