Also note that the magnetic headings of runways are not always exact. Magnetic variation (shown as isogonic lines on Sectional Charts) also changes over the years. Many airports over a long period of time have had to scrape the numbers off their runways because the magnetic variation shifted the runway heading.
Magnetic headings are also rounded up or down when runway numbers are created, so if the heading of a runway is 164 it would be runway 16, while a magnetic heading of 166 would be rounded up and be dictated runway 17.