Dear All,
Recently, although it was not mentioned by name, there has been a lot
of discussion about the efficiency of soft conversion during a metric
transition.
Examples were:
* Listing the drive shaft on a socket spanner as 1/2" — instead of the
true design dimension and the true make dimension of 12.7
millimetres. This is a sure way to continue the discussion about the
metric vs old pre-metric measures question for 100 years or more.
Good metrication plans have statements like:
'If parts have to be chosen to match old heritage standards, then the
part will be specified in the equivalent metric units — the name of
the old pre-metric measure should not be mentioned ever again. It
should not be used in any calculation and it should never be written
down.
Here are some examples of soft conversions that have been discussed on
this list:
* Tyre (tire) sizes are designed and measured during manufacture using
metric sizes (e.g a wheel is designed rim is measured as 356
millimetres to meet an old pre-metric specification of 14 (1959
metric) inches) then that size should be specified in metric units to
the nearest whole number of millimetres; in this example as 356 mm.
It's bad enough having to accommodate heritage measures without also
having the problem of generating heritage disputes as well.
* Although print definition is mostly hidden by never mentioning any
units at all, the recurrence of dpi gives credibility to a measure
that is rarely used or recognised. This might be a great opportunity
to reconsider the whole issue of image definition pixels, and the way
these are measured and calculated.
* Nominal pipe sizes are now, and always have been, based on absolute
lies. They were either intended to deceive or, if they happened by
accident, it has been continued for decades for deceptive purposes. It
is a completely irrelevant topic and there should be no need for
anyone in the world to ever consider such nonsense, For example, the
use of nominal pipe sizes does not conform to American Standard pipe
designations. See http://www.engineeringtoolbox.com/nps-nominal-pipe-sizes-d_45.html
to find out about real, current, and relevant world standards using
millimetres.
* Some automotive parts (such as a front disc brake rotor) suffered
from a 'soft conversion' in the 1970s when (say) an 11 inch disc
became a 280 millimetre during the worldwide metric transition in the
automotive industry that was known as developing the 'world car'
concept in the 1970s.
Soft conversions are always subject to pressure to reversion for as
long as they can be recognised as soft conversions. I shudder to think
of the cost of all the discussion that soft conversion generates
through constant recalculation of the old equivalent pre-metric
measure, the correction of the mistakes converting to the old measure,
and the constant discussion about generated questions like: Why don't
we finish the metrication? or This is silly why don't we go back to
the old days? Maybe I should raise the estimate of how much it costs
the USA not to go metric; see http://www.metricationmatters.com/docs/CostOfNonMetrication.pdf
!
However, some government agencies go soft on soft conversions, such as
the U.S. Department of Transportation Federal Highway Administration
at http://www.tfhrc.gov/pubrds/summer95/p95su14.htm (see 1995 quote
below). Perhaps they have not had enough experience with the
metrication process to know that soft conversions almost always fail.
Hiding soft conversions with consistently applied metric specification
helps a little, but soft conversions are best avoided altogether or
only ever used as a stop gap to give you time to rethink the old sizes
and to use the opportunity of the metrication process to redesign, to
rationalise wastes and to reduce costs.
"Hard" Versus "Soft" Conversion
The federal government makes a distinction between "hard" and "soft"
conversions to the metric system. A soft conversion is a direct
mathematical conversion from a U.S. measurement to its metric
equivalent e.g., from 180 pounds to 81.65 kilograms. A hard conversion
is the creation of a new, rounded, rationalized number that is easy to
work with and easy to remember.
FHWA encourages the use of hard conversion as much as practicable.
Where hard conversions have not been established, however, state
highway agencies should use soft conversions. The bottom line is that
a project should not be delayed simply because some hard conversions
have not been developed yet.
Several agencies, including FHWA, have adopted the American Society
for Testing and Materials (ASTM) manual E380 as the standard for
making metric conversions. An excellent reference is the Metric Guide
for Federal Construction published by the National Institute of
Building Sciences.
By the way, in the next paragraph, the U.S. Department of
Transportation Federal Highway Administration makes it absolutely
clear that they believe that the way forward to metrication is through
encouraging as much metric conversion as they can.
Efforts are not standing still between conferences. The ideas
generated in conference are being put into action. Other FHWA metric
training and education efforts include the following:
FHWA has developed and distributed more than 150,000 metric/U.S.
measurement conversion slide rules to its field offices, state highway
agencies, technology transfer centers, and other appropriate offices.
Two of FHWA's regional offices have developed computer conversion
programs for general use. These programs have been distributed
agencywide and are available on FHWA's electronic bulletin board.
FHWA developed and has made available a computer software program that
can be used within WordPerfect to convert U.S. measurement units to
metric units.
FHWA has developed and made available a metric poster and a metric
cube (a small box with metric conversion information on all six sides).
As most of you know, I consider the metric conversion process to be so
slow, socially painful, and expensive that I would never recommend it
to any organisation. See http://www.metricationmatters.com/metric_conversion.html
and also http://www.metricationmatters.com/docs/ApproachesToMetrication.pdf
where I rate metric conversion little higher that ignoring the whole
process and hoping it will go away!
Cheers,
Pat Naughtin
PO Box 305 Belmont 3216,
Geelong, Australia
Phone: 61 3 5241 2008
Metric system consultant, writer, and speaker, Pat Naughtin, has
helped thousands of people and hundreds of companies upgrade to the
modern metric system smoothly, quickly, and so economically that they
now save thousands each year when buying, processing, or selling for
their businesses. Pat provides services and resources for many
different trades, crafts, and professions for commercial, industrial
and government metrication leaders in Asia, Europe, and in the USA.
Pat's clients include the Australian Government, Google, NASA, NIST,
and the metric associations of Canada, the UK, and the USA. See http://www.metricationmatters.com
for more metrication information, contact Pat at [email protected]
or to get the free 'Metrication matters' newsletter go to: http://www.metricationmatters.com/newsletter
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