Stupid question, maybe.

In Bentley, it lists the spark plug gap for my 84 1.9L waterleaker as 0.28"
+ 0.004"

Why the '+0.004"?' Does this mean the gap should actually be 0.32"?

I bought the standard Bosch plugs from Bus Depot. Are they pre-gapped? They
seemed to be about 0.28"

Thanks!

Steve