Prixone, YOU are NOT calculating the fucking PR, GOOGLE do it, it is a freaking TRADEMARK made by GOOGLE, nobody knows how's it's EXACTLY calculated but in a nut-fucking-shell, the more links from quality sites (with high PR) you have the higher are chances your PR will go up.
And, how THOSE SITES calculate PR?-THey Fucking Don't, they use the motherfucking tools (let's call those tools GOOGLE plugin) to tell you what PR did Google gave you during the last PR update or whatever...DO, you fucking get it or you want me to continue?