How to modify carbon film resistor to reduce its resistance value

Take a carbon film resistor with a slightly larger resistance than the one you need. Replace the red and black test leads of the multimeter with red and black alligator clips. Use the red and black alligator clips to clamp the resistor to be changed, use a knife or blade to scrape off the protective paint on the resistor, and then gently scrape the exposed carbon film a few times. Then use a pencil to rub back and forth on the carbon film while watching the resistance value indicated by the multimeter. At this time, you will see that the resistance value is gradually decreasing, and finally you can get the resistance value required by the lock.

It is worth mentioning that no matter which of the above situations is the case, a layer of paint or quick-drying glue should be applied on the scratched or pencil-spitted areas of the resistor as insulation to prevent the carbon film from getting damp and causing the resistance value to change.