N_{1} |
= first critical speed, RPM |

N_{2} |
= second critical speed, RPM |

??_{1} |
= static deflection, (in, m) at W_{1} if shaft is horizontal |

??_{2} |
= static deflection, (in, m) at W_{2} if shaft is horizontal |

E |
= modulus of elasticity (young's modulus), (psi, N/m^{2}) |

d |
= diameter of shaft, (inches, m) |

W_{1} |
= load applied to shaft, (lbs, Kg) |

I |
= Area Moment of Inertia , (in^{4}, m^{4}) |

l |
= distance between centers of bearings, (inches, m) |

a |
= distance from bearings to load, (inches, m) |

b |
= distance from bearings to load, (inches, m) |