A simple puzzle once you learn how to apply this set of three numbers for the cache. (Bay:Column:Row)
Bay:
When you enter the Post Office you will find multiple walls with post office boxes. A normal group of boxes is about 6 feet tall by 6-8 feet wide; each of these groups are considered a Bay for this puzzle. The number of the bay is calculated by counting Bays from from left-to-right.
Column:
Counting from left to right (from within the Bay #), the leftmost box is Column 1 and the next box from the left is Column 2 and continuing on to the right of the Bay.
Row:
Starting at the upper left corner of the Bay and counting from top to bottom (from within the Bay #), the top Row is 1 the next Row down is 2 and continuing on to the bottom of the Bay.
Warning, sometimes the box size changes, but the count will not.
All that is left is to plug in the P.O. Box number, for Bay, Column, Row into that particular spot in the cache coordinates below and complete the simple calculation.
To find the cache location, use the (Bay:Column:Row) format.
N39º 38.ABC W084º 13.DEF
ABC=[(B1:C3:R3) x (B2:C2:R5)] - [(B3:C1:R5) x (B1:C1:R4)] + [(B3:C6:R5) / (B1:C1:R5)] - [(B2:C8:R3) - (B2:C4:R1)]
DEF=[(B3:C4:R3) x (B2:C1:R1)] - [(B3:C7:R2) x (B1:C3:R2)] - [(B3:C6:R4) / (B1:C2:R3)] - [(B2:C9:R1) x (B1:C2:R4)]
The Post Office lobby is open 24 hours. The cache location can be found at night. Please be careful at the final location at night, so that you don't appear suspicious to potential onlookers.
Please do not remove cache and bring your own writing tool.
Good luck and have fun!
You can check your answers for this puzzle on GeoChecker.com.