High: units

• mil vs. metric
  • 1 inch = 25.4 mm -> too large
  • 1 mil = 0.001 inch = 0.0254mm
  • usual imperial values: 100 mil, 10 mil, 8 mil: 2.54 mm, 0.2032 mm, 0.254 mm
• Result: mm only, mil only, mixed
• file format may support multiple; but internally there is normally only one
• reasonable precision; example:
  • gEDA/PCB: 1mil ('90s), 1/100mil (2000s), nm (2011)
  • PowerPCB: 2/3 nanometer
• double vs. Fixed Point integer vs. base unit
• angle: deg vs. radian vs. "steps"
  • steps (N*90): gEDA/PCB
  • integer degree (Eagle xml)
  • 0.3 degree (Eagle bin)
  • 0.1 degree (PowerPCB)
  • error: 0.1 degree on 100 mm radius: 0.17 mm error!

Imperial: Myanmar, Liberia, UK/2, USA