In computer science's object-oriented programming, class variables (static fields) contain information which is associated with all instances of a class. If all tanks have one cannon, then it is not necessary to specify, in an instance variable for each tank object, that each tank has only one cannon; rather, one can simply define a class variable which does this and thus all instances of the class will share the variable.
... For every 100 females there are 95.1 males. For every 100 females age 18 and over, there are 89.3 males.
The median income for a household in the town is $75,076, and ...