text: The Sommerfeld Number is typically defined by the following equation:
  where:
  : S is the Sommerfeld Number or bearing characteristic number
  : r is the shaft radius
  : c is the radial clearance
  : µ is the absolute viscosity of the lubricant
  : N is the speed of the rotating shaft in rev/s
  : P is the load per unit of projected bearing area
  The second part of the equation is seen to be the Hersey number. However, an alternative definition for S is used in some texts based on angular velocity:
  where:
  : is angular velocity of the shaft in rad/s.
  : W is the applied load
  : L is the bearing length
  : D is the bearing diameter
  It is therefore necessary to check which definition is being used when referring to design data or textbooks, since the value of S will differ by a factor of 2π.