Historical anchor price calculation

Hello, I would like to know how is calculated the "Historical anchor price" (anchorPrice) in the APC-RPO.

There is a function to do this calculation:

anchorPrice, minHistPrice, maxHistPrice, MaxPrcUpPcnt,MaxPrcDownPct<- ApcRpoAnchorPrice(ancMask,price,priceover, anchPrNumPer, anchPrSmthCo, minPrQuint, maxPrQuint, minMaxNumPer, pz2prlocmap, htstrtidx, htendidx)

This measure is sent to RPO, and used as a "Original Price/Current Price".

Really what I need to know is, how can I explain what means this measure ("Historical anchor price") to the final user? (from the point of view of RPO)

Many Thanks,

Helio Nunes.