ISO standard requires the volume to be read at the lowest point of the liquid level. This lowest point has to touch the upper limit of the graduation mark. Meniscus is the curvature in the surface of the liquid. The curvature is caused by the surface tension of the iquid. On the volumetric glassware the shape of the meniscus is concave (curved downwards). For accurate and most precise results the eye of the observer must be at the same level to the meniscus. To get a better, faster and recise reading and measurement a black strip should be help at the back, just below the graduation mark and meniscus line.