A system for deriving a value representative of central aortic systolic pressure comprising: an arterial waveform measuring device; and a processing unit, wherein, the arterial waveform measuring device is arranged to take a blood pressure (bp) measurement at predetermined intervals until at least one arterial waveform is represented by a set of blood pressure measurements taken, the set of blood pressure measurements being representative of one arterial waveform then being communicated to the processing unit, the processing unit including: a) means for reversing the order of the blood pressure set to obtain a reversed blood pressure set (rbp), the reversed blood pressure set being representative, of a reversed arterial waveform determined according to the following formula: rbp 1... n = bp n... 1 wherein: bp represents the set of blood pressure measurements rbp represents the set of reversed blood pressure measurements and (n) is the predetermined number, characterised in that the processing unit further includes; b) means for determining an integer interval value (i) calculated by dividing the predetermined number (n) by the time taken to complete the arterial waveform to form a sampling rate (sr) which is divided by a predetermined division value (v) to determine the integer interval value (i); c) means for repeatedly averaging a series of consecutive reversed blood pressure measurement readings in a reversed blood pressure set equal to the integer interval value (i) commencing from a q th reversed blood pressure measurement in the reversed blood pressure set, wherein the averaging means sets the value of q commencing at 1 and increments the value of q by 1 each time until the value of q plus the integer interval value (i) minus 1 equals the number of blood pressure measurements in the average set; d) means for storing the averaged reversed blood pressure measurements in an average set; e) means for identifying a point of intersection on the reversed blood pressure set and the average set; and f) means for setting the value representative of the central aortic systolic pressure (CASP final) as the reversed blood pressure value CASP A in the reversed blood pressure set nearest to the point of intersection. an arterial waveform measuring device; and a processing unit, a) means for reversing the order of the blood pressure set to obtain a reversed blood pressure set (rbp), the reversed blood pressure set being representative, of a reversed arterial waveform determined according to the following formula: rbp 1... n = bp n... 1 wherein: bp represents the set of blood pressure measurements rbp represents the set of reversed blood pressure measurements and (n) is the predetermined number, characterised in that the processing unit further includes; bp represents the set of blood pressure measurements rbp represents the set of reversed blood pressure measurements and (n) is the predetermined number, characterised in that the processing unit further includes; b) means for determining an integer interval value (i) calculated by dividing the predetermined number (n) by the time taken to complete the arterial waveform to form a sampling rate (sr) which is divided by a predetermined division value (v) to determine the integer interval value (i); c) means for repeatedly averaging a series of consecutive reversed blood pressure measurement readings in a reversed blood pressure set equal to the integer interval value (i) commencing from a q th reversed blood pressure measurement in the reversed blood pressure set, wherein the averaging means sets the value of q commencing at 1 and increments the value of q by 1 each time until the value of q plus the integer interval value (i) minus 1 equals the number of blood pressure measurements in the average set; d) means for storing the averaged reversed blood pressure measurements in an average set; e) means for identifying a point of intersection on the reversed blood pressure set and the average set; and f) means for setting the value representative of the central aortic systolic pressure (CASP final) as the reversed blood pressure value CASP A in the reversed blood pressure set nearest to the point of intersection.