A level uncertainty question

Previous part of question if it’s relevant:

The resolution of the stopwatch may well be 0.01s but that is not the uncertainty in the measurements.

You have to remember that the operator of the watch has to 'guess' when the needle passes 10V and again when it passes 5V.
You have to take into account the time it takes you to react and press the button.
If you only made one measurement you would have to estimate this. It could be around 0.1s for start time and again 0.1s at the stop.
This would give an estimated uncertainty of 0.2s

However, the person has taken repeated measurements, which helps to reduce this error.
You can see from the results that the highest value was 12.16V and the lowest was 11.94V

The estimated uncertainty for this would then be half the difference between the highest and lowest values.
Check it out.
This is the usual way of estimating uncertainty for repeated measurements at A-Level.