You can use relative coordinate input (e.g. @3,0, @3<30, ...) or use the "line with given angle" tool or draw a line that is longer than what you need and trim it later. Depends on your exact situation.
i think i can use the angle tool, but i am not satisfied. i think this must be the priority tool to upgrade. if i want a specific measure its very useful to check first point than with mouse point the direction off the line free or orto and simply input a number refer for length. angle must be 0 by default and only input angle when needed, because angle is not the priority!