A system for evaluating a vessel of a patient, the system comprising: a processor configured to: obtain a first series of pressure measurements from a first instrument within the vessel over a time period while the first instrument is moved longitudinally through the vessel from a first position to a second position; obtain a second series of pressure measurements from a second instrument positioned within the vessel over the time period while the second instrument remains in a fixed longitudinal position within the vessel; calculate a series of pressure ratio values using the first pressure measurements and the second pressure measurements; generate a pressure ratio curve for the time period using the series of pressure ratio values; identify a stepped change in the pressure ratio curve using an automatic step detection process, the automatic step detection process including: identifying a general position of an ending point of the stepped change by identifying a change in the pressure ratio values within a first window along the pressure ratio curve that is at or below a first threshold change value; identifying an optimized position of the ending point by identifying a change in the pressure ratio values within a second window along the pressure ratio curve that is at or below a second threshold change value, wherein the second window is smaller than the first window, and the second threshold change value is smaller than the first threshold change value. a processor configured to: obtain a first series of pressure measurements from a first instrument within the vessel over a time period while the first instrument is moved longitudinally through the vessel from a first position to a second position; obtain a second series of pressure measurements from a second instrument positioned within the vessel over the time period while the second instrument remains in a fixed longitudinal position within the vessel; calculate a series of pressure ratio values using the first pressure measurements and the second pressure measurements; generate a pressure ratio curve for the time period using the series of pressure ratio values; identify a stepped change in the pressure ratio curve using an automatic step detection process, the automatic step detection process including: identifying a general position of an ending point of the stepped change by identifying a change in the pressure ratio values within a first window along the pressure ratio curve that is at or below a first threshold change value; identifying an optimized position of the ending point by identifying a change in the pressure ratio values within a second window along the pressure ratio curve that is at or below a second threshold change value, wherein the second window is smaller than the first window, and the second threshold change value is smaller than the first threshold change value. obtain a first series of pressure measurements from a first instrument within the vessel over a time period while the first instrument is moved longitudinally through the vessel from a first position to a second position; obtain a second series of pressure measurements from a second instrument positioned within the vessel over the time period while the second instrument remains in a fixed longitudinal position within the vessel; calculate a series of pressure ratio values using the first pressure measurements and the second pressure measurements; generate a pressure ratio curve for the time period using the series of pressure ratio values; identify a stepped change in the pressure ratio curve using an automatic step detection process, the automatic step detection process including: identifying a general position of an ending point of the stepped change by identifying a change in the pressure ratio values within a first window along the pressure ratio curve that is at or below a first threshold change value; identifying an optimized position of the ending point by identifying a change in the pressure ratio values within a second window along the pressure ratio curve that is at or below a second threshold change value, wherein the second window is smaller than the first window, and the second threshold change value is smaller than the first threshold change value. identifying a general position of an ending point of the stepped change by identifying a change in the pressure ratio values within a first window along the pressure ratio curve that is at or below a first threshold change value; identifying an optimized position of the ending point by identifying a change in the pressure ratio values within a second window along the pressure ratio curve that is at or below a second threshold change value, wherein the second window is smaller than the first window, and the second threshold change value is smaller than the first threshold change value.