Why my sites PR updated twice in 10 days

I noticed get an increased PR last week for two of my sites.
but today both sites PR go back.
any one tell me why?

 

may be some data center redundancy !!

 

Yea check your pagerank on digpagerank.com and some of the datacenters has your New pr and your old PR

 

Maybe you were penalized.

 

He wasn't penalized. The PR checker your looking at is taking info a datacenter with the last PR info.

 

This is fully dependent upon google algorithms.

Suppose, you may get backlink from one good high pagerank page for some days then google will give you good page rank for that time period and then may be your link will be removed from that site and google may crawl same page again and it didnt fine it again so google may decrease your page rank.

 

there is some delay time for google.