An apparatus comprising: a body having an inlet and an outlet defining a fluid flow passageway; a flow control member interposed between the inlet and the outlet to control a pressure of the fluid at the outlet; and a filter disposed between the inlet and the flow control member; characterized in that: the apparatus further comprises means for measuring a parameter of the fluid across the filter, the means for measuring comprising a detector having: a first measurement point upstream of the filter, the detector measuring a first pressure at the first measurement point via a first channel formed through the body of the regulator that fluidly connects the detector and a chamber formed in the body upstream of the filter; and a second measurement point downstream of the filter, the detector measuring a second pressure at the second measurement point via a second channel formed through the body of the regulator that fluidly connects a detector and a bore formed in the body downstream of the filter; wherein the detector measures a pressure difference between the first measurement point upstream from the filter and the second measurement point downstream from the filter and upstream from the flow control member. a body having an inlet and an outlet defining a fluid flow passageway; a flow control member interposed between the inlet and the outlet to control a pressure of the fluid at the outlet; and a filter disposed between the inlet and the flow control member; characterized in that: the apparatus further comprises means for measuring a parameter of the fluid across the filter, the means for measuring comprising a detector having: a first measurement point upstream of the filter, the detector measuring a first pressure at the first measurement point via a first channel formed through the body of the regulator that fluidly connects the detector and a chamber formed in the body upstream of the filter; and a second measurement point downstream of the filter, the detector measuring a second pressure at the second measurement point via a second channel formed through the body of the regulator that fluidly connects a detector and a bore formed in the body downstream of the filter; wherein the detector measures a pressure difference between the first measurement point upstream from the filter and the second measurement point downstream from the filter and upstream from the flow control member. the apparatus further comprises means for measuring a parameter of the fluid across the filter, the means for measuring comprising a detector having: a first measurement point upstream of the filter, the detector measuring a first pressure at the first measurement point via a first channel formed through the body of the regulator that fluidly connects the detector and a chamber formed in the body upstream of the filter; and a second measurement point downstream of the filter, the detector measuring a second pressure at the second measurement point via a second channel formed through the body of the regulator that fluidly connects a detector and a bore formed in the body downstream of the filter; wherein a first measurement point upstream of the filter, the detector measuring a first pressure at the first measurement point via a first channel formed through the body of the regulator that fluidly connects the detector and a chamber formed in the body upstream of the filter; and a second measurement point downstream of the filter, the detector measuring a second pressure at the second measurement point via a second channel formed through the body of the regulator that fluidly connects a detector and a bore formed in the body downstream of the filter; wherein the detector measures a pressure difference between the first measurement point upstream from the filter and the second measurement point downstream from the filter and upstream from the flow control member.