Printed in a non-reproducible blue ink on Alva-Line blue-white quality tracing paper, the isometric grids are clear, sharp and accurate, yet won`t reproduce on Diazo prints. All grids are printed on reverse side of sheets to prevent removal during erasure. These medium weight (16# basis, .00275 thickness) pads are professional quality, ideal for use by engineers, draftsmen, architects, graphic artists, etc. 50 sheets to a pad, in two sizes.