To counter the perception that all of us in scientific fields use metric exclusively, here are a few more examples of how in electronics work we have no problem with using more than one system of measurement.

JACK PLUGS: The full-size version is 1/4 inch. When miniature types came in from overseas, they were dimensioned in millimeters. We quite happily talk about a 1/4" plug while referring to the smaller types as 3.5 and 2.5mm. Some British (and Australian) suppliers that have gone "metrically correct" now insist on calling the traditional jacks 6.35mm. I have NEVER heard anybody actually say something like "Could you pass me one of those six-point-three-five millimeter jacks please?" It's too much of a mouthful, and everybody already knows them as "quarter-inch jacks."

DIL INTEGRATED CIRCUITS: Pins are on a 0.1" spacing.

MAGNETIC TAPE: Specified as 1/4", 1/2", 1" etc. The tape length is specified in feet and the spool size in inches, e.g. 1200 ft. on a 7" spool. Tape speed is specified in inches per second, the standard speeds going up in powers of two: 1 7/8 ips, 3 3/4 ips, 7 1/2 ips, 15 ips, 30 ips. European specifications do often use cm/sec, but quite often round them to 9.5, 19, 38 cm/sec etc. The ips specifications are EXACT, however, so the correct metric speeds are 9.525, 19.05, 38.1 cm/sec.

FUSES: The glass type used in almost all older equipment (and some new) is 1 1/4" in length by 1/4" diameter. The smaller type comes from Continental specifications and is 20 x 5 mm. Thus we quite happily refer to both a "One-and-a-quarter inch fuse" and a "Twenty millimeter fuse." Again, some British suppliers do list the former as 32mm now, but you'd have a hard time finding anyone who actually calls them that.

OSCILLOSCOPES: Tube diameter is traditionally measured in inches, but the markings on the graticule are centimeter squares. The centimeter just happens to be a convenient size for this purpose, and results in simple designations such as V/cm (volts per centimeter).

PHONOGRAPH CARTRIDGES: Tracking force on modern units is very light and is conevniently measured in grams. The old metric dyne is also used in calculations. But the stylus tip radius is normally specified in mils (typically 0.5 to 1 mil for LPs).

That's enough technicalities. I'm just making the point that in some scientific fields at least, we have no problem with mixing systems of measurement.

Perhaps the predominence of non-metric units in these fields has something to do with America, pre-metric UK and their influence on this technology.

The catalogue of mixed units given above proves just how messy things can be. It certainly doesn't look elegent.

I don't doubt that's the case.

The point is that the mix of units doesn't really cause problems in most cases. Take the jack plug ezample for instance.

The actual diameter of the jack is really only of great significance to anyone who is designing and manufacturing them. To those of us who are just using them, saying "quarter inch" or "three and a half millimeter" is no different than using any other adjective, such as "standard" or "miniature."

You say Paul that it doesn't cause problems. I say that it could do potentially.

Why do we need both inches and cm?

We don't *need* both, in the sense that we could measure quite well with one or the other.

It's just that both systems have come to be used over the years, and in these particular cases the different units are convenient for different things.

"Why do we need both inches and cm?"

We don't "need"

And guess what? Most people just get on with it - mixing measures all the time for purely convenient reasons free from the state!

If mixed units are convenient then surely there is an underlying need.

But that vague statement about convenience needs clarification.

And what's the state got to do with it?

I as an individual I can see the sense of a single rational system of measurement. I don't need state politicians to tell me that.

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If mixed units are convenient then surely there is an underlying need.
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The underlying need is to avoid the pain of converting everything that is in one system to eliminate it.

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And what's the state got to do with it?
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The states nowadays get involved in a lot of thigs that could get along fine without them. Why does the state need to build roads anyways? Companies could build them, there would be tolls instead of taxes, and supply and demand would rule.

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I as an individual I can see the sense of a single rational system of measurement. I don't need state politicians to tell me that.
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Yes there is sense in that. But not enough to justify the cost of conversion.

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And what's the state got to do with it?
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If a dispute arises about a measurement, then it will be resolved in a courtroom. The courtroom must turn to some authority to get a ruling on the measurement. Since time immemorial, that authority has been the state.

For example, I buy some bananas from a trader. We agree the units and we agree the price. I then accuse him of using scales that give short weight. His says his scales are in order. Who should arbitrate - that is the state's job which is why the state sets the rules for weights and measures.

You are quite right of course Martin, there are circumstances involving contractual agreement where state intervention may arise.

The reason for my question was the remark made by SteveH. It implied a political agenda for using a single system of units in circumstances where plain commonsense would favour it.

Thanks anyway to you and to others for the various thoughts.