When you are using the Line or Area feature, there is a way you can get a perfectly straight line with every click of the mouse.
Option #1 - If you hold down the Shift key on your keyboard, the software will go into an "ortho" mode where it gives you a perfectly striaght line. If you take your finger off of the Shift button, you can move in any direction.
Option #2 - If you hold down the Shift key and tap the letter "O" on your keyboard, the ortho mode will turn on and stay on until you hit the Shift-O a second time. If you are measuring and 90% of the lines are straight and you have 1 diagonal line, you can hold down the Shift button once you reach the diagonal line. This will turn off the ortho mode for that one click. When the diagonal line is in, you can take your finger off of the Shift key and the software will go back into the ortho made.