Are there any caches that vary in location, either by coordinates or by altitude?
This could either be deliberate or not.
An example would be a cache placed on a ferry or a bus with a fixed route.
Also a fixed location but a variable altitude, for example, a cache
placed on an elevator in a 40 story building!
In those casesd, the cache description may need to specify a range of coordinates
or a range of altitudes.
A severe example could be a cache on an inclined railway that changes both in altitude
and by coordiantes, simultaneously!
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