Can someone provide a reference to the mathematical formula we use for Pressure Ripple on an HPLC? In particular I'm wondering about the meaning of negative pressure ripple, which I have seen a couple times now on our HPLCs; I thought that pressure ripple looked at the absolute value of the change of pressure, which makes the meaning of negative ripple a little murky. Ordinarily we look for pressure ripple below a certain threshold; if the value is negative I presume we would just take its absolute value?
