can anyone provide advice / an explanation?
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Jeff,

You obviously suffer from Index Fatigue.
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On a analog dial plain markers are called indices (the plural of index). I also call them ticks.

Indices require an additional mental process to convert them into a number which is useful. By themselves they are no more informative than a scratch on the crystal.

That is why dials with Arabic numbers ( Roman are no better than ticks) are so appealing especially after an extended wearing of index marked watches.

The Pilot type watches are the best because the dark background and lighter numbers offer wonderful contrast.
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Im sorry to say your condition is not curable. However it may be alleviated by periodically purchasing a nice watch with numbers on the dial. See pic for suggestions.

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