What is the DIfference between HIL and HFOM(EPU).?

Question

What is the difference between HIL(Horizontal integrity limit) and HFOM(horizontal figure of merit ) also called as EPU(Estimated position uncertainity).I could understand what EPU is but why do we need HIL when we already have EPU.Please do answer this.

Answer 1

A few questions for you.  What are you looking at?  Is this an aircraft component?  What country are you from?  What type of aircraft?  Sounds like some sort of navigation equipment.  Please explain what it is.

Answer 2

huh?