Mostly what was said above. General rule of thumb is low mag means it is not needed. Parallax adjustment only really comes into it with larger magnifications (think 9x and above) If 3-9 etc not really needed, but a 6-24x it would be a good idea. For what you describe as purpose, I would agree a 2-8, 2-7 or 3-9 would be fine without parallax adjustment.
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