The Recommended Practices Committee of the International Society of Philosophical Engineers' Universal Law for Naive Engineers
Law #1: In any calculation, any error which can creep in will do so.
Law #2: Any error in any calculation will be in the direction of most harm.
Law #3: In any formula, constants (especially those obtained from engineering handbooks) are to be treated as variables.
Law #4: The best approximation of service conditions in the laboratory will not begin to meet those conditions encountered in actual service.
Law #5: The most vital dimension on any plan drawing stands the most chance of being omitted.
Law #6: If only one bid can be secured on any project, the price will be unreasonable.
Law #7: If a test installation functions perfectly, all subsequent production units will malfunction.
Law #8: All delivery promises must be multiplied by a factor of 2.0.
Law #9: Major changes in construction will always be requested after fabrication is nearly complete.
Law #10: Parts that positively cannot be assembled in improper order will be.
Law #11: Interchangeable parts won't.
Law #12: Manufacturer's specifications of performance should be multiplied by a factor of 0.5.
Law #13: Salespeople's claims for performance should be multiplied by a factor of 0.25.
Law #14: Installation and Operating Instructions shipped with the device will be promptly discarded by the Receiving Department.
Law #15: Any device requiring service or adjustment will be the least accessible.
Law #16: Service conditions as given on specifications will be exceeded.
Law #17: If more than one person is responsible for a miscalculation, no one will be at fault.
Law #18: Identical units which test in an identical fashion will not behave in an identical fashion in the field.
Law #19: If, in engineering practice, a safety factor is sent through the service experience at an ultimate value, an ingenious idiot will promptly calculate a method to exceed said safety factor.
Law #20: Warranty and guarantee clauses are voided by payment of the invoice.
Law #21: The rule for engineers: "Change the data to fit the curve."