[jtf]

I purchased a 25ml Class A Volumetric Flask from Amazon.
Using a precision balance (Mettler Toledo) where the balance is super accurate in the 25g range; and was professionally calibrated two weeks prior,  I wanted to test the accuracy of the score on the flask.
The room was at 75F
I used distilled water.
When I added 25g of distilled water to the flask, the bottom of the meniscus is between 1.5mm-2mm above the score line on the volumetric flask. The flask has a posted rating of +/- .03, so I would assume that at 25g that +/- is equal to  .03ml so the weight of distilled water the score should be 24.97 to 25.03, but it's much higher.

Can someone help me to understand why a Class A glassware would be off by so much? I also tested a 15ml Class A flask and the results were similar. I would be grateful for any assistance. As mentioned, the balance was professionally calibrated by MT just two weeks prior and has not experienced any real weighing activities since then.

Pics on this Google Page:  https://docs.google.com/document/d/1l6Z5aR7iq6Dqi4d4wJmYKyzughlIV-ozahoP86RKTuk/edit?usp=sharing

Thank you.

[hypervalent_iodine]

Would it not be better to fill to the line of the flask and weigh it? That way you have a more precise idea of how off it actually is. Also worth noting that the density of water is not exactly 1.00 g/mL, so you should take that into account when you do your calculations.

[jtf]

Thanks for the idea. I think filling to the line and weighing it is a great idea, but we need to know what is the displacement to the line. 
If the scale is exceptionally accurate, and if the volumetric flask is Class A and should have a fine tolerance, then which is most likely the source of the error? What is the best way to figure this out? Buy a calibration weight and use that as the 25g standard to see if the score line is accurate?

Thank you much.

[Borek]

If you need high accuracy you should calibrate the glassware:

http://www.titrations.info/volumetric-glass-calibration

What is water density at 75 F? Have you accounted for that?

[jtf]

Thank you. I will re-measure using the correct water density calculations at the given room and water temp.