BillJ writes:

I thought I understood everything that could be on a sectional, but
before a trip to New York City airspace, I studied the sectional and
terminal area charts a little extra carefully. Just southwest of Newark
(EWR) (and also other places) there is a notation such as 70/+12 in blue
for the floor and ceiling of class B airspace. What does the "+" mean?

Above, but not including 1200 feet MSL, presumably (although I've never seen
this myself).