VPIP and Call Open?

If you are an experience HEm user...what is the difference with VPIP and Call Open? And does anyone use Call Open effectively?

I think it's their raise calling percentage. hah i hope i'm right =) i find this stat very useful and have it on the main HUD. After vpip and PFR%.

VP$IP is voluntarily put money in the pot; this is whenever someone pays to see the flop. You open a pot by being the first to raise PF, so anyone that calls this raise will get that stat added to.

vpip is where you raise, call a raise or limp preflop. Call open (or 'cold call pf' in pokertracker) is where you call a raise pf.

thanks guys..Im thinkn about starting to put call open on my hud..hope it helps

i think it means they call a bet and open with a continue bet on the flop