A DimensionedVariable contains both a value (any valid numeric type) and units (any combination of mass, length, time, etc.). Math operations performed on DimensionedVariables will automatically perform dimensional analysis to ensure that units are consistent.
In my experience this tool has helped me reduce units-related errors, has made my code much easier to understand, and has also generally sped up my work.
New for this version: easily switch to using a different base unit system and work in any base unit system you like, e.g. English units (default is still SI).
Rob is responsible for the foundation of this submission: http://www.mathworks.com/matlabcentral/fileexchange/10070