Precompiled version for Windows 64-bit and 32-bit; linux 32-bit. Source included for others.
Instructions:
Download the precompiled version (or compile the source):
Extract its contents.
Copy the .dll into your $TEC_360_2009/bin or $TEC_FOCUS_2009/bin directory (Windows) or $TEC_360_2009/lib directory (Linux)
Edit your tecplot.add file and append this line:
$!LoadAddon "MeasureDistance"
Start Tecplot
A "Measure Distance" option will appear in the Tools menu option:
Use 2 clicks to measure distance. After the second click, the distance is reported, giving you the option to create a geometry to show where you clicked.
When in 3D, a 3D polyline geometry is used that cannot be interactively manipulated. (In other words, you can change its color, but you cannot move it.)
File: (right-click and save)
Windows 64-bit and 32-bit DLLs, Linux 32-bit library and source: MeasureDistance.zip