I calibrated torque wrenches and gauges at a research center.
1. Do not ship your torque wrench. It will be worse than when you sent it.
2. Fastenal would be good if you could walk it in and walk out with it.
3. Clicker types are just as accurate as digital and can be repaired easier.
4. Comparing to other torque wrenches is ok as long as you use a smooth pulling motion and same person does both or 3 torque wrenches is better. Birdtracker