Hey there! That's a fantastic question that every plant engineer should ask before diving into an automation upgrade. The 'hidden costs' of retraining maintenance staff can really sneak up on you if you're not careful. Let me break down how to calculate these costs in a practical way.

First, you need to think beyond just the training course fees. The real hidden costs come from:

1. **Productivity Loss During Training**: When your maintenance staff is in training, they're not fixing things. Calculate their hourly wage × training hours × number of staff. For a typical PLC course (24-40 hours), this adds up fast!

2. **Learning Curve Downtime**: After training, there's a period where staff are less efficient. They'll troubleshoot slower, make more mistakes, and need more support. Industry estimates suggest 3-6 months of reduced efficiency - calculate this as reduced productivity percentage × staff costs.

3. **External Support Costs**: You'll likely need vendor support or consultants during the transition. Budget for emergency support calls and on-site assistance.

4. **Training Materials & Equipment**: Beyond course fees, you'll need PLC hardware for hands-on practice, software licenses, and reference materials.

5. **Ongoing Training**: PLC platforms evolve! Factor in annual refresher courses and updates to stay current.

A good rule of thumb: The hidden retraining costs often equal 25-40% of your initial hardware investment. So if you're spending $100k on PLC equipment, budget another $25-40k for the full retraining impact.

The key is to track these costs as part of your Total Cost of Ownership (TCO) calculation - it's the only way to get the true picture of your automation upgrade's real price tag!