blunt measures

In the book " The Financial Times Guide to Social Media Strategy" the author talks about the metrics of reaching audience, such as views, impressions, "These are all fairly blunt measures of social media performance and comes with a health warning. Social media measurement can be opaque and occasionally leads many to question the legitimacy of the data."
What does "blunt" mean in "blunt measures"?

The writer has chosen the wrong metaphor. Measures for implementing a policy might be blunt (incapable of or unsuitable for fine work), but measures used for measuring things are coarse (incapable of precise measurement).

It means they don't give very accurate indications of performance.

Cross-posted with UJ.