@edezzie wrote:
.... If I draw an ordinary line 200mm ortho mode applies. But if I type 200mm when drawing a linear dimension ortho mode does not apply.
You can do this with Object-Snap Tracking [F11]. It takes a little getting used to, but is quite powerful. The following works even on non-orthogonal edges, which suggestions involving Ortho would not.
Have Endpoint or Midpoint and Perpendicular set as running Osnap modes, and Osnap Tracking on.
Start a DIMLINEAR [if the edge is orthogonal] or DIMALIGNED [whether or not it is] command, and pick the definition endpoints.
Hover the cursor over an endpoint or the midpoint of the edge, so that the little grab-it marker appears, and haul the cursor out in the direction you want the dimension line to be located.
Take it in a direction so that the Perpendicular Osnap icon appears on that reference point, and you're locked into the direction perpendicular to your edge. Type in 200.
You may see more than just the one Osnap-Track alignment indicator, depending on where the cursor is, whether it's grabbed a definition point other than the one you're going from, and what your Polar angle increment setting is. If you're getting some you don't want, you can hover over the points they're radiating from to "un-grab" those as Tracking reference points, and narrow it down to just the one point.
For a non-orthogonal edge, depending on the angle and what other Osnap modes you may have on, you may see the icon at your Tracking reference point change with small changes in cursor position. Make sure you type in your distance when the Perpendicular icon is showing.
Kent Cooper, AIA