You take full responsibility for their use. Use these pointers as annotations to the published criteria. Systematic implies some regularity. Taking readings at 18C, 20C, 25C, 60C, 70C would not qualify. Accuracy and reliability are paramount.
Many students draw a graph as a matter of course, but make no further reference to it.
They should be encouraged to look closely at and comment on their own method and their actual results. E6a - anomalous results are most easily spotted by looking for points on a graph that don't quite 'fit'. Results are often relatively few and not always reliable - this should be reflected in the firmness of their conclusion. Suggesting an alternative technique to check the results is more sensible.