English/metric measurement error in the Mars Climate Orbiter

**mklotz** · Apr 15, 2019, 11:03 AM

Originally Posted by tonyfoale

Apart from the decimal nature of the ISO metric system the thing that I like the best is the consistency of the units. If you forget what certain derived units are you only have to use the base units of kg, m and sec to get reminded.

What is a newton - we know it is a force and as F=ma a N must be kg.m/sec^2
What is a joule - it is work so it has to be force x distance which is Nm. So 1 joule = 1 Nm
What is a watt - it is power so it has to be work/time which is joule/sec or Nm/sec So 1 watt = 1 joule/sec = 1 Nm/sec
What is a pascal - it is pressure so it has to be force/area which is N/m^2 So 1 pascal = 1 N/m^2

That is as simple as it gets. This consistency of the units reduces the chance of errors greatly.

While the inferial system has such idiocies as "fluid-ounce" which is a measure of volume, not weight.

Do not just think of the ISO metric system as being only a decimal system, it goes much further than that.

For more on that, folks can visit my essay...

http://www.homemadetools.net/forum/g...1486#post93973

**tonyfoale** · Apr 15, 2019, 11:54 AM

Originally Posted by mklotz

For more on that, folks can visit my essay...

http://www.homemadetools.net/forum/g...1486#post93973

Marv,

I do not recall reading that previously but I see that I posted a comment there so I must have seen it.
That echos my thoughts exactly. Everyone here should read it.
I grew up with imperial measurements and non decimal currency. I had to wait for a change to decimal currency, that was decided by higher powers but once I left formal education I became a metric convert. That is the ISO metric system, metric land was not always so clear with different base units being used in different fields presumably dictated by the size of the things being measured. For example c,g,s and m,k,s systems. I have seen recent papers still using the c,g,s even a mixture of c,g,s and m,k,s - confusion guaranteed.

PS. A note for those unfamiliar with non-decimal British currency.
Instead of a large base unit like the $ and two decimal places to cater for smaller amounts, the British and Australian system had three units of currency.
Viz: Pounds (£), shillings (s) and pence(d). Yes pence was "d", "p" took over only when the UK went decimal. In addition pence was further divided to get the halfpence (often pronounced happ'ny) and the farthing.
The three units of money is not necessarily a problem, the problem (maybe stupidity is better) was the relationship between them
4 farthings to a penny
2 halfpence to a penny
12 pennies to a shilling
20 shillings to a pound

A totally disproportionate amount of time in arithmetic classes was spent on teaching currency addition, subtraction, multiplication and division.
Imagine ordering 37 milling cutters at £5 3s 8d ea. How long will it take you to calculate the total?
OK let's try to make it easier, surely 10 off instead of 37 is easier? Think so, try it.