Update Operation

[poryagrand]

Hi, I'm having trouble understanding what the "update" operation does. Does it add volume, remove volume, or update the volume of an order? How can I differentiate these actions within the update operation in the market depth function? Thank you.hi . i can't understand what operation "update" do!
is it adding volume? removing volume? updating volume of an order?
how can differ these from one update operation in market depth function?
thanks