Clearing "fog" from glass measuring cups

try a good 'soap scum' remover for showers/tubs -- CLR also if you have a high mineral content in your water

Try soaking in vinegar, if it is really layered on, it may take some time and scrubbing. It also depends on if they are etched or just water residue. If they are etched it will never come off and you will need to get new ones to read the markings.

soke in vinegar for a few hours. Should remove fog. Use a permanent marker to replace the measurements on the out side.

vinegar

Vinegar is definitely the solution

Try scrubbing them with white toothpaste. It works for car headlights.