Do not use a digital scale as they often will not respond to the door weight changing as rollers no longer stick to the track.
How to chage springs on garage door.
One at the end of each spring and one at the top of the vertical door track they also have two cables on each side.
Use a piece of tape to mark the current placement of the pulley so that it.
Once in place disconnect the garage door opener.
Take up the left garage door spring and put it by the left side of the door.
Doors with extension springs have two sets of pulleys which are sometimes called sheaves.
Place the new garage door springs against the garage door position the springs so that the ends are facing you and coming from opposite directions.
Open the garage door to remove all spring tension and clamp it in place.
Place scale under the garage door on the side of the door with the broken extension spring.