Drilling personnel need to fully understand about the lag time. Lag time is time delay from pressure adjustment made on a choke valve or a choke HCR to show up on the drill pipe pressure gauge.
Does it sound confuse? Let’s me explain more about it. When you adjust a choke position, you will not be able to see changes on the drill pipe gauge right away because drilling fluid is compressible so you need to be patient and wait a little bit until you see the changes on the drill pipe gauge.