By definition, the Earth's surface is planar.

for the area under consideration, i.e. a hundred mile trip.

An ICBM has no navigation system.

"ballistic" means "ballistic"



There's no outside reference when using DR to navigate.

deduced reckoning is navigating by compass and knot log. neither are outside
references as to position

It costs $15,000/year to make 10gals of water/day with a shipboard
watermaker.

Don Casey says it is a dollar a gallon. The cost accountants would give the
higher figure, in the context of the problem under then discusssion.

etc.