Lab rat here: The plastic labware is more accurate because the measurements are molded in; all of the graduated cylinders, for example, are the same size. Glass ware is more variable because it is extremely difficult to make identical glassware (the more you pay, the more accurate the glassware becomes). A typical glass beaker, for example, will vary from all of its siblings in the same case. At any rate, the scientific glassware is printed with the measuring scale by a machine, so it isn't very consistent. Kind of like your cheap/new measuring plasticware. Even though the plastic measuring cups are molded and probably fairly consistent in size, the stamp with the "levels" for the various amounts kind of just gets applied in random ways. Hope this makes sense.

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