1.Is this caliper have the Fraction unit?
Yes, the caliper could be switch the unit between inch,fraction.
2.How many battery come with the package? and what type of the battery?
One installed and one extra included. it’s the 3V CR2032 battery.
3.The caliper with IP54 waterproof, Can it be use under the water?
IP54 can just protects against dust, splashing water and grease so please dont use the caliper in water.