Linear transform to map a value in one range to a value in another.

transform.js

function scale( value, old_top, old_bottom, new_top, new_bottom )
{
  // minTo + (maxTo - minTo) * ((value - minFrom) / (maxFrom - minFrom))
  return new_bottom + ( new_top - new_bottom ) * ( ( value - old_bottom ) / ( old_top - old_bottom ) ); 
}