9 doesn't have built-in scale bars (yet), nor does it have a built-in grid (yet). Both are coming.
In the interim, whenever I want a "snap to grid" I create a drawing that has a grid of points at regular intervals, and then when I draw lines or areas I can snap to those points. Copy the objects drawn and paste to their own drawing and they are still aligned to the grid. You can do that with points as well, by providing an attribute so that all the grid points have "grid" in that field.
This allows making the grid points transparent, so the effect is exactly the same as snapping to a grid. But I usually prefer to style my grid points as very small, thin stroke crosses, so I can see them as a reference grid when drawing. This is a fine technique when using 9 as a ersatz CAD program. Use it to draw landscape designs, whip up a floor plan for a new structure, etc.
OK. Use that technique to create lines that are however long you want them, with cross bars at the end. If you have good skills and muscle memory with Manifold editing, all that is very easy and very fast. If you don't have good skills it's a puzzle.
Here's an example of how using good skills you can in seconds create a horizontal line that is 1 km long:
1. create a point.
2. Select that point and Copy it. Deselect. [That's a Ctrl-A, Ctrl-C, Shift-Ctrl-A]
3. Use Transform - shift set to 1000 m in the X direction and apply. The point moves.
4. Ctrl-V to paste.
You now have two points 1 km apart. Draw a line between them (it snaps). Done.
Style as desired, with begin and end perpendiculars, for example, and then move it around using the usual editing commands (Shift-Alt-Click, select all the coords, and drag as desired) into your view. You can even label it like a scale bar "1 kilometer".
The technique of copying a point or set of points and then shifting them, pasting in their former place what was copied is very effective for creating grids, if you want to do that manually and not via SQL. You just double the number of points every time when you move them.
Suppose we used the above process to make points 1 m apart. Copy them, shift them 2 m in the X direction, paste, and we now have four points that are 1 m apart horizontally. Repeat with a larger shift and you have eight. Do that ten times and you have 1024 points. Repeat in the vertical direction and you have a 1024 x 1024 grid of points. Tedious, but it only needs to be done once, and anybody who does it once can post the result to this forum.
Or, use 8 just once to make a grid of points :-)