There is no official "formula sheet" for the Astronomy C event. I believe you are referring to the sheet on the Scioly.org website (http://scioly.org/wiki/images/c/c6/Formula_Sheet.pdf), which was made by competitors, not event supervisors. However, there are helpful formulae and examples on the Coaches Manual CD.
When grading numerical answers, supervisors always should accept a range of answers, usually plus or minus 10% of the value on the key. This guideline is shown on the sample tests at http://soinc.org/sites/default/files/uploaded_files/Astronomy_ES_GUIDE_C15.pdf and http://soinc.org/sites/default/files/uploaded_files/AnnotatedRegionalAstronomyTest15.pdf. A nominal range can be explicitly due to competitors having slightly different physical constants or tabulated values depending on their resource.
(section: 3 / paragraph: c / sub-paragraph: i / line: 2)