This magnetic seam guide helps you guide the edge of your fabric as you sew at whatever seam allowance you require.  

It's a great tool for a creating a straight line or circle lines. Just drop the magnetic edge guide onto your machine bed or slide plate and it will stay in place, it can be used to set edge guides quickly. It has a strong magnet and does not move easily.

And yes, it can be used with computerized machines as long as you place it on the plate beside the presser foot and not on other parts of the machine.