Program Setup and Preferences
AutoCAD out of the box is not ready for professional production work. Fix that first.
Why this matters
Default AutoCAD settings are designed for the broadest possible user base, which means they're optimized for no one in particular. Wrong units mean your world is scaled incorrectly. Wrong linetype scale settings mean your dashed lines look different in every viewport. Wrong right-click behavior means you're fighting the interface instead of using it. Set these up once, correctly, and they stop being problems.
Critical settings
Type OPTIONS (or OP) to open the Options dialog. Spend time reading every tab before changing anything — understanding what each setting controls is more valuable than memorizing which ones to click. The settings below are the ones that matter most for this course.
| Command | Setting | Why |
|---|---|---|
UNITS | Architectural · Inches · 0'-0 1/64" precision | Your drawings are in feet and inches. Everything in model space is drawn at real-world scale. If units are wrong, every measurement and scale factor in the drawing is wrong. |
LTSCALE | Start at 1 — adjust per drawing scale | Global linetype scale. A dashed line that looks correct at 1"=20' will look wrong at 1"=100'. You will revisit this whenever you change drawing scale. Note that annotative scales will adjust this automatically. |
PSLTSCALE | Set to 0 | Controls whether linetypes scale per viewport or globally. Set to 0 means each viewport controls its own linetype display — which is what you want when a sheet has multiple viewports at different scales. |
OPTIONS → User Preferences → Right-click | Repeat last command | Right-click repeating the last command is one of the most efficient habits you can build. You will use it hundreds of times per session. Consider setting time-sensitive right click so you still have the menu as an option. |
OPTIONS → Open and Save | Autosave: 10 minutes | CAD crashes happen. Autosave is not a substitute for saving manually, but it is a backup for the moments you forget. |
OPTIONS → Files → Printer Support File Path | Point to Dave_Purdue.ctb location | AutoCAD needs to find the pen settings file. If it can't, everything plots at default lineweights. Load the CTB file location once per machine setup. |
Units and scale — the principle
AutoCAD's model space is unitless — it operates in abstract drawing units. What gives those units meaning is the UNITS setting. With Architectural units, one drawing unit equals one inch. When you draw a line 120 units long, you have drawn a 10-foot line. Everything in model space is drawn at full scale: a 200-foot road is drawn as a 200-foot road. Scale happens in paper space, when viewports project model space content onto a sheet at a defined ratio.
If you ever inherit a drawing that looks tiny or enormous, measure a known object with DIST or ID. If your 10-foot wall measures as 10 units but should be 120 (inches), the drawing was created in Engineering or Decimal units and needs to be scaled by a factor of 12.
Try this
Open AutoCAD and type OP. Read every tab in the Options dialog without changing anything. Note what you don't understand. Then look those things up. Come back and set the items in the table above. Draw a rectangle that is 20 feet wide by 30 feet deep. Verify with DIST that it measures 240 units × 360 units. If it doesn't, your units are wrong.
What breaks
Wrong UNITS setting is the most damaging setup error. A drawing created in Engineering units (where 1 unit = 1 foot) and then XREFed into an Architectural units drawing (where 1 unit = 1 inch) will appear 12× too small. Everything that references that XREF inherits the problem.
PSLTSCALE = 1 means linetypes are scaled globally — a dashed property line that looks correct in one viewport will look completely different in any viewport at a different scale. Always set PSLTSCALE to 0.