The Recomended Practices Committee of the International Society of Philosophical Engineers' Universal Laws for Naive Engineers:

Law 1
In any calculation, any error that 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 veriables.

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 requsted 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 specification of performance should be multipled by a factor of 0.5.

Law 13
Salespeople's claims for performance should be multiplied by a factor of 0.25.

Law 14
Instalation and Operating Instructions shipped with a device will be promptly descarded by the Reciving 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 feild.

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 methoud to exceed said safety factor.

Law 20
Warranty and garantee clauses are voided by payment of the invoice.