Excel Formula Halving Hours

I have a multi-sheet training tracker in Excel where each trainee’s progress is logged manually in several hour-related columns (Task Started, Part-Trained, Fully Trained, etc.). What I cannot crack is a single formula that will pull every trainee’s true training-time total—regardless of which sheet the record sits on—and then return exactly half of that figure.

Here is the landscape:
• Data lives across multiple worksheets in the same workbook; sheet names follow no set pattern.
• Hours are always typed in by hand.
• A trainee may have more than one hour column, but the last “Fully Trained” value represents the completed total. Typical totals run anywhere from 20 up to 40+ hours.
• The end result I need to display on a summary sheet is 50 % of that completed total, calculated automatically.

Your job is to craft an elegant, workbook-wide formula (or an array-friendly spill solution) that:
1. Locates each trainee’s final “Fully Trained” value, even if it appears on a different sheet.
2. Returns half of that value to my summary table in real time.
3. Works for any future sheets I add without manual editing.

Please deliver the ready-to-paste formula along with a short note explaining any named ranges or dynamic functions you use so I can maintain the file going forward.