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.