A method for replacing a process measurement instrument comprising: operating a process under pressure; providing a first measurement instrument mounted with respect to a measuring assembly positioned for measuring a parameter associated with the process, removing the first measurement instrument from the measuring assembly while the process operates under pressure; and replacing the first measurement instrument with a second measurement instrument while the process operates under pressure by installing and mounting the second measurement instrument with respect to the measuring assembly , wherein the first measurement instrument includes a first coupling attached to and plumbed inline with the first measurement instrument , the first coupling configured to allow a user to remove the first measurement instrument from the measuring assembly via removing only the first coupling from the measuring assembly while the process operates under pressure without substantial loss of fill or sensing media from the first measurement instrument , wherein the second measurement instrument includes a second coupling attached to and plumbed inline with the second measurement instrument , the second coupling configured to allow the user to replace the first measurement instrument by mounting the second measurement instrument with respect to the measuring assembly via the second coupling while the process operates under pressure, the method characterised in that the first and second couplings are dry-break couplings and by the second measurement instrument : (i) containing pre-filled sensing media configured to react to pressure of the process, and (ii) pre-charged to a pre-determined pressure level. operating a process under pressure; providing a first measurement instrument mounted with respect to a measuring assembly positioned for measuring a parameter associated with the process, removing the first measurement instrument from the measuring assembly while the process operates under pressure; and replacing the first measurement instrument with a second measurement instrument while the process operates under pressure by installing and mounting the second measurement instrument with respect to the measuring assembly , wherein the first measurement instrument includes a first coupling attached to and plumbed inline with the first measurement instrument , the first coupling configured to allow a user to remove the first measurement instrument from the measuring assembly via removing only the first coupling from the measuring assembly while the process operates under pressure without substantial loss of fill or sensing media from the first measurement instrument , wherein the second measurement instrument includes a second coupling attached to and plumbed inline with the second measurement instrument , the second coupling configured to allow the user to replace the first measurement instrument by mounting the second measurement instrument with respect to the measuring assembly via the second coupling while the process operates under pressure, the method characterised in that the first and second couplings are dry-break couplings and by the second measurement instrument : (i) containing pre-filled sensing media configured to react to pressure of the process, and (ii) pre-charged to a pre-determined pressure level. <EOS>