You could consider using the adverb vaguely which means:
In a way that is uncertain, indefinite or unclear; roughly.
Or roughly if your context includes difficult and even unpleasant pronunciation:
In a manner lacking refinement and precision
[Oxford Online Dictionary]
The issue is your scale/grid using adverbs doesn't seem ideal because it is not easy to tell the difference between hardly and vaguely or other suggested adverbs, not to mention between fairly and easily.
Therefore, it is better to scale a grid using a number, i.e. from 1 to 5 or 1 to 10 with an explanation such as "Scale 5 (or 10) representing perfectly (100%) intelligible".
Then, it becomes more clear and objective than using those adverbs which are understood based on personal subjective judgement.