Using Two Monitors Makes You More Productive?

Double Vision asks: "In my job, I work with several software applications at once. I find that constantly switching back and forth wastes a tremendous amount of time and causes me to lose focus. My video card supports two monitors, so I found a discarded monitor in my office and hooked it up. This has made it much easier to do my job. However, we are getting ready to go through an equipment audit, which means I will likely lose my additional monitor unless I can justify keeping it. How can I make this case? Is anyone aware of studies that support my claim that two monitors makes me more productive?"