A method of moving a string assembly within a wellbore is disclosed. In some embodiments, the method comprises moving the string assembly within the wellbore; obtaining surface data regarding at least one parameter associated with moving the string assembly within the wellbore over a range of depths; modeling the at least one parameter over the range of depths for a plurality of assumed friction factors to obtain modeled data for each assumed friction factor; calculating a derivative of the surface data over the range of depths; calculating a derivative of the modeled data over the range of depths; comparing the derivative of the surface data to the derivative of the modeled data; determining one or more local friction factors for the range of depths based on the comparison; and adjusting at least one string assembly operating parameter based on the one or more local friction factors.