“NVM” is an open source software tool for making precise neuroanatomical measurements in MRI.  “SegMentor” is a feature of this software that explicitly defines and embeds measurement methods into the tool by providing on-line, context-sensitive instructions and definitions, and also by assisting in making the measurements.  SegMentor records, plays, and allows viewing and editing of scripts that provide information to the user and also control the rest of the program.  We present the results of a study to analyze the effectiveness of SegMentor for increasing the reliability and decreasing the time necessary for making precise neuroanatomical measurements.  By analyzing the same brain scans with and without using SegMentor, we show improvements in both accuracy and efficiency:  using SegMentor increases the repeatability and decreases the cost to obtain quantitative MRI brain measurements.