There are a number of different ruler types that allow you to change the length/direction of lines.
Tape Measure Type Rulers
Place you finger on the tape measure and pan left or right to change the length measured by the ruler. Placing 2 fingers on the ruler and pinching will change the scale of the teeth on the ruler. Tapping on the Course/Medium and Fine can achieve the same effect.
The Red line indicates the Ruler measurement. When you lift your finger off the ruler the ruler will snap to the nearest tooth to the red line.
When editing a line, it is drawn in blue.
The end of the line that is changed when the ruler is moved is highlighted in red.
Create New Lines
This ruler allows you to change the length of a line whilst adding new lines.
Update Line Length
This ruler allows you to change the length of an existing line.
This ruler allows you to change the scale of the current page of the sketch.
This ruler allows you to create eaves for a property. To create a new eave, tap on the lines for which you want it to be created. Changing the measurement on the ruler will change the size of the eave being created.