It just reminded me to post about my Gridrunner Measuring tool (ruler) i made for CadSoft's Eagle PCB which is available for download in the files section
I noticed in the Beta they have included a measuring tool at long last, but alas I found it is still not the best. Although you can always move the zero mark (0,0) but often you would just like to take a quick measurement between 2 points and keep zero intact. Another way was to move the PCB points to zero but still it's awkward when taking quick measurements.
This is where the Gridrunner ruler comes in its basically a custom library which you add just like any other PCB component but you get a groovy 200mm ruler in 10th of a millimeter increments you can fly around the PCB taking measurements very accurately and quickly by eye .
Eagle can be used for other forms of CAD other than just PCB layouts when you bring the "dxf.ulp" into action and this is where the Gridrunner ruler really came into its own measuring complicated layouts.
Not being up to speed with other leading CAD packages such as AUTOCAD I often make front panels to scale simply because it's quicker for me to use one package I know for multiple purposes, then use them as cutting templates.
Presently I am designing the mechanical side of my CNC machine using Eagle Cad then exporting it as a DXF. Once you have learnt how to make a library it's pretty quick to make whole parts in Eagle which enables you to move things around until you get a working layout. This is what I did for each of the purchased mechanical parts in Eagle for my CNC machine; each part can be moved as a whole which makes aligning easy and also throws up any gotchas with your design.
After the parts are aligned I can mark out the drill holes and dimensions of the plates to be cut. Once the other components are removed and exported to DXF they can in turn be used for CAM or sent for CNC or laser cutting, minimizing waste - 19mm thick Aluminium plate doesn't come cheap!
The only limit in Eagle is the work space! which maxes out around 1 meter which is fine for the stuff i do .