You can't look at it as nute burn because that would appear much differently as you are aware. This on the other hand is a complete burn across all nutrients. The below copy and paste is just one of many examples of the issue. If you don't think my leaves look quite like that then that is another issue and perhaps you are correct about deficiency?
As for my meter I calibrate it once a week and it never drifts more than .05 from true. I just bought a new one to be able to double check accuracy and it came off by .25 for gods sake. I checked them both against GH calibrating solution and I keep all my pens in water now and they stay much more accurate.
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Over Fertilising!
Figure 4 is definitely an over fertiliser problem. The high level of nutrients accumulates in the leaves and causes them to dry out and burn up as shown here. You must flush with clear, clean water immediately to allow the roots to recover, and prevent further damage. The find the cause of the high nutrient levels.
I didn't capitalize that, it came that way, that would seriously be rude.