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Almost certainly, however, what is happening is that the database doesn't have information on the keywords you are using and returns zero as a result.
If you feel that the keyword is a good one, don't be scared off by the Traffic Estimator. Just enter the keyword, and see how it performs in 'real life'.
Not a bad idea to monitor frequently. In case it turns out to be a really low CTR word, you can catch it before it becomes a problem.
Why be so secretive about keyword impressions?