How can my Acer Aspire adjusting the zoom level, all the time?

My Netbook Acer Aspire is great, but for some reason, change the zoom level to use the mouse (this screen zoom from 100% to between 10% to 200%. I right click on it, without success, and I think which is the standard provides that. Unfortunately, there is a sensitivity that the command is driving me crazy! Help please, thanks.