What are Isobars?

An isobar is a line drawn, on a weather map, joining all places having the same atmospheric pressure at the time for which that weather map was drawn.

It is important to note thet atmospheric pressure is dynamic – it may change frequently. Hence its value, when stated, holds hold only for that particular time.
For statandardisation, isobars are drawn at 4 mb intervals and the pressure denoted by an isobar must be divisible by 4 i.e. 996,1000, 1004 etc. where consecutive isobars are very far apart, intermediate isobars at 2 mb intervals may be inserted and the readings should be according to UTC and not ship’s time.
Isobars cannot cross or meet because one place cannot have different values of atmospheric pressure at the same time.