buttman wrote:

2) On sectional charts, the tops of class D and class C airspace is
listed as either [45] or [-45], meaning "up to and including 4,500ft",
and "up to but not including 4,500ft" respectively. I'm wondering,
whats the point of distinguishing between the tow? I assume one means
basically "from the ground to 4,500ft", while the other one means
"from the ground to 4,499ft". Whats the point?


The reason for having the distinction is because it is
most likely due to the fact that the D or C airspace is
underlying class B (or some other) airspace which is in
effect exactly at 4,500. its easier to say -45 than 4499.9

You can instruct without having a valid medical IF you
are not acting as PIC or required crew. I'm trying to
think if that's even possible in a typical small airplane
scenario. But you always must have a valid Commercial
license for the CFI to be valid. ATP can give instruction
as well for type ratings.