Hi, could someone give me an explanation of what is PF(t) in schedule management ?

It's a term from Earned Schedule similar to Performance Factor (PF) in EVM. In EVM you use CPI and SPI for actual performance compared to plan. Those are essentially efficiency factors.

Like EVM compares work planned to work actually completed, Earned Schedule uses the time planned vs. the time expended.

PF(t) is an estimated future efficiency rather than basing it on past performance (SPI). SPI and CPI are performance factors based on prior data (Actual performance/Planned). If you think your performance will remain as it was, you can use SPI to estimate remaining time. If you think your SPI will change, you can use different performance factors to estimate the remaining time to complete the work.

This page has the comparisons between the formulas for the 2 methods:
https://www.earnedschedule.com/terminology.shtml

thank you Keith, that's crystal clear
I think an update of the document p88 would be useful to add the information that PF(t) is the Performance Factor and how it could be calculated. I don't know whom to contact for that ......