I should really explain the dial and hands first before I get to the pump.
The yellow inner ring is just a rotating dive time display.
The outer ring displays the depth scale in meters.
The yellow hand is the maximum depth indicator. The white hand is the current depth indicator.
NOW, comes the tricky part. The pump.
The pump only pumps air into the mechanism to check for pressure. To check the accuracy of the depth indicator, simple as. The maximum depth level on the watch can be tested with several pushes of the pump. When the yellow hand reaches maximum, it will remain there. The test is here - when releasing the pump, if the white flyback current depth hand drops below the 'zero' mark, the depth gauge need to be calibrated.
Some people do get confused about the pump's functions.
So, basically, as you give deeper and deeper the white current depth hand fluctuates according to the depth you're in.
Phew...
Pana