Digital scratch pad?

<p>I use a lot of scratch paper in maths/physics and I was wondering if there's such thing as "digital paper" where I can just perform scratchwork like on real paper, and erase it as easily as throwing out paper. I don't need something fancy like an iPad since I'm not going to be using it for anything else, but the iPad screen looks kind of small to be a scratch pad (8"x11.5" like real paper is a good size).</p>

<p>The second result of my search for "Digital scratch pad" on Google came up with one. I'm sure other results have more.</p>