The Staedler Mars Plastic Combi is a premium quality eraser that can be used on a variety of surfaces and media.
The blue 1/3 is for drawing ink on paper and matt drafting film. 2/3 of the eraser is white and can be used to take off lead residue; both coloured and graphite.
It is an accurate and versatile tool which has minimum crumbling and absolutely no smudging.