Why does screen on Surface Pro 3 magnify or shrink unintentionally as I use tourch pad?

[Windows Central Question]

I will move my finger on touchpad of my SP3 and suddenly my app has either grown larger or shrunk. Often the size makes it unusable. It seems related to moving my finger sideways and could be that I might have a finger from my other hand on the pad at the same time, but now I'm guessing. When I try to repeat the action that caused the change, most often I am unable to cause the screen to resize. It all seems so random, and I need to control this.