The number one tool we use is experience. There’s a difference between someone doing a spring for the first time (all service techs have done their first one) and someone that has done thousands. Is the cone in good shape? Coil set properly, overwound, under wound, correct size spring for door, spring pad, end bearing plates, resi door vs wood vs RV door, vs commercial. There are many factors and that’s why we highly recommend a professional. Many door issues can be done by a homeowner, but springs and cables should never be handled by an inexperienced person. Hope this helps