Go to menu bar > View and open up the size and position window. Draw a
line, then, with the line still selected, entire the desired value in the
length box. Then, if you desire, right click the line to bring up the
context menu > Format > Protection and lock the width. (Technically, a line
has no height, since it is a 1-D shape.)
If you lock the line length, you can still rotate it thru the size and
position window (and change it's length.) To fully lock the line, you will
need to open it's shapesheet, then scroll down to the Protection section, and
set the entry for LockVtxEdit to "1" (without the quotes0>
