Edsel Murphy's Laws

General

1. In any field of scientific endeavor, anything that can go wrong, will.
2. If the possibility exists of several things going wrong, the one that will go wrong is the one that will do the most damage.
3. If nothing can go wrong, something will.
4. Left to themselves, things always go from bad to worse.
5. Nature always sides with the hidden flaw.
6. Given the most inappropriate time for something to go wrong, that's when it will occur.
7. Mother nature is a bitch.
8. If everything seems to be going well, you have obviously overlooked something.
9. Never make anything simple and efficient when a way can be found to make it complex and wonderful.
10. If it doesn't fit, use a bigger hammer.
11. In an instrument of device characterized by a number of plus-or-minus errors, the total error will be the sum of all the errors adding in the same direction.
12. In any given calculation, the fault will never be placed if more than one person is involved.
13. All warranty and guarantee clauses become void upon payment of final invoice.

Design

1. In any given price estimate, cost of equipment will exceed estimated expenditure by a factor of 3.
2. Dimensions will always be expressed in the least useable terms. For example, velocity will be expressed in furlongs/fortnight.
3. If the breadbox trial model functions perfectly, the finished product will not percolate.
4. In a mathematical calculation, any error that can creep in, will. It will be in the direction that will do the most damage to the calculation.
5. In any given computation, the figure that is most obviously correct will be the source of error.
6. The probability of a dimension or value being omitted from a drawing is directly proportional to its importance.
7. In specifications, murphy's law supersedes ohm's.

Assembly

1. If a project requires n components, there will be n - 1 components available.
2. Interchangeable parts won't.
3. Components that must not and cannot be assembled improperly will be.
4. The most delicate component will be dropped.
5. The construction and operation manual will be discarded with the packing material. The garbage truck will have picked it up five minutes before the mad dash to the rubbish can.
6. The necessity of making a major design change increases as the assembly and wiring of the unit approach completion.
7. A dropped tool will land where it can do the most damage (also known as the law of selective gravitation).
8. A component selected at random from a group having 99 per cent reliability will be a member of the 1 per cent group.
9. Tolerances will accumulate unidirectionally toward maximum difficulty of assembly.
10. The availability of a component is inversely proportional to the need for that component.
11. If a particular resistance is needed, that value will not be available. Furthermore, it cannot be developed with any series or parallel combination.
12. After an instrument has been assembled, extra components will be found on the bench.

Wiring

1. Any wire cut to length will be too short.
2. Milliammeters will be connected across the power source, voltmeters in series with it.
3. The probability of an error in the schematic is directly proportional to the trouble it can cause.

Test

1. Identical units tested under identical conditions will not be identical on the final test after being buried under other components.
2. A self-starting oscillator won't.
3. A crystal oscillator will oscillate at the wrong frequency - if it oscillates.
4. A p-n-p transistor will be found to be an n-p-n.
5. A fail-safe circuit will destroy others.

Operation

1. If a circuit cannot fail, it will.
2. A transistor protected by a fast-acting fuse will protect the fuse by blowing first.
3. Probability of failure of a component is inversely proportional to the ease of repair or replacement.

Trouble Shooting

1. After the 24th cabinet-to-chassis screw has been removed to replace the under chassis fuse, it will be observed that the line cord plug has become disengaged from the a.c. receptacle.
2. After the 24th cabinet-to-chassis screw has been assembled, the driver tube will be found under the schematic on the bench.
3. The bleeder resistor will quit discharging the filter capacitors as the operator reaches into the power supply enclosure.

Programming

1. In any program, any error which can creep in will eventually do so.
2. Not until the program has been in production for at least six will the most harmful error be discovered.
3. Any constants, limits, or timing formulas that appear in the computer manufacturer's literature should be treated as variables.
4. The most vital parameter in any sub-routine stands the greatest chance of being left out of the calling sequence.
5. If only one compiler can be secured for a piece of hardware, the compilation times will be exorbitant.
6. If a test installation functions perfectly, all subsequent systems will malfunction.
7. Job control cards that positively cannot be arranged in improper order will be.
8. Interchangeable tapes won't.
9. If more than one person has programmed a malfunctioning routine, no one is at fault.
10. If the input editor has been designed to reject all bad input, an ingenious idiot will discover a method to get bad data past it.
11. Duplicated object decks which test in identical fashion will not give identical results at remote sites.
12. Manufacturer's hardware and software support ceases with payment for the computer.
13. At least one critical test tape will be lost, misplaced, destroyed or written over.
14. What goes up must come down - and can be expected to do so in the middle of your job.

Finagle's Laws

1. No matter what result is anticipated, there is always someone willing to fake it.
2. No matter what the result, there is always someone eager to misinterpret it.
3. No matter what happens, there is always someone who believes it happened according to his pet theory.

Finagle's Creed

Allen's Axiom

Gunnersen's Law

Glasser's Corollary

The Finagle Factor

That quantity which, when multiplied by, divided by, added too or subtracted from the answer which you got, yields the answer you should have gotten.

Some vital things to remember when doing lab work

1. When you don't know what you are doing, do it neatly.
2. Experiments must be reproduceable. They should fail the same way each time.
3. First draw your curves, then plot your data.
4. Experience is directly proportional to equipment ruined.
5. A record of data is essential. It shows you were working.
6. To study a subject best, understand it thoroughly before you start.
7. To do a lab really well, have your report done well in advance.
8. If you can't get the answer in the usual manner, start at the answer and derive the question.
9. If that doesn't work, start at both ends and try to find a common middle.
10. In case of doubt, make it sound convincing.
11. Do not believe in miracles-rely on them.
12. Team work is essential. It allows you to blame someone else.

Further hints on write-ups

1. In any collection of data, the figures that most closely confirm the theory are wrong.
2. No one you ask for help will see the mistakes either.
3. Everybody who stops by with unsought advice will see them immediately.
4. If an experiment works, you must be using the wrong equipment.
5. An experiment may be considered successful if no more than half the data must be discarded to agree with the theory.
6. No experiment is ever a complete failure. It can always serve as a bad example.