Using the right way: volumetric flasks
Volumetric flasks are used for correct preparation of solutions.
1-First step is to add the exact quantity of the product inside the flask. Then fill the flask with distilled water HALF of the flask and mix the content.
2-Then, carefully, fill with water until you see the volume level BUT try not to tocuh the sign.
3-Get the content to 20°C temperature.
4-Add some drops of distilled water so the meniscus should be at the same level with the mark.
5-Read very carefully the volume level - the eyes and the mark shoud situate at the same height. Check the flask neck not to be still wet so there could be some additional drops of liquid.