How can I see whether I am supposed to take a measurement in cVitals today?

FocusCura -

Once you have logged into cVitals, you will see a list of the day's measurements. If you see a blue bubble next to the measurement value, this means that you still need to take a measurement.

If you do not need to take a measurement, the message ‘Not necessary’ will appear next to the bubble (colored white). You are always free to take an additional measurement.