Simplify the following text for a Grade 9 native English-speaking person.
Original: The symbol for degrees Rankine is Â R ( or Â Ra if necessary to distinguish it from the RÃ mer and RÃ aumur scales ) . Zero on both the Kelvin and Rankine scales is absolute zero , but the Rankine degree is defined as equal to one degree Fahrenheit , rather than the one degree Celsius used by the Kelvin scale .
Simplified: The Kelvin and Rankine temperature scales are defined so that absolute zero is 0 kelvins ( K ) or 0 degrees Rankine ( Â R ) .