Fraction Circles and Clock

Here you can use a clock to measure fractions in a fraction circle.

When you press the "show me how" button, you can see how the clock can be compared to the angle. The part of the circle that matches the angle will be entered into the "hours" text box.

Click "my turn" if you want to try matching the same angle again. Click "next" to try a new angle.

Which fractions cannot be measured in hours?