change values of dimension.

As a beginner, I have created a square using the command line and dimensioned the sides by using the aligned dimension tool with the mouse, found out this was only approximately the true length. Tried to modify with tool-modify-properties and unlike lines, no option for changing the dimension only thickness of line etc. Is there a way to do this so the dimension is exactly the line length.

You probably didn't have "Snap on Endpoints" on.

OK thanks, but as a rank beginner where do I find snap on end points.

1. Start on the forum main page and find the link to the manual.
2. Enter snap in the Search docs field on the left side and hit ENTER
3. Click on the 1st search result Snapping
4. Find Snap on Endpoints in the table and notice its icon
5. Find the icon in LibreCAD's Snap Selection tool bar, usually at the bottom of the Window
6. If the icon isn't there, enable the Snap Selection tool bar in the menu Widgets -> Toolbars

Optional: use the command se, which is also noted in the manual, on the LibreCAD command line