Horrible Experiments

There are four mandatory experiments to do with Heat on the leaving cert syllabus.
And we always do them.
And, apart from the first, they can all give horrible (and I mean horrible) answers.

I warn the troops in advance and suggest that a percentage of under 30% would be acceptable. It's not unusual for a student to get a percentage error greater than 100%.
But they generally don't calculate this untill they are writing up the experiment at home.
They don't ask about it in class because they probably think that they would just be highlighting their own incompetence, and I don't mention it because I also am a little embarassed by their results, knowing that they were only following my instructions.

Am I the only teacher who is this inept?
Do many others check?
What do I know? As I keep saying, in this business once we close that classroom door we become kings of our own classroom, and it wouldn't be unusual for a teacher to go from their own secondary school as a student, up until the day they retire, having only ever seen one other person (their old science teacher) teach any given topic.
This can't be right.
Can it?