M2
difficulty or confusion using either.
volume, requiring 4 L (+/- 0.25 L).
People can then say 4 L when
Our new general rule is to use m or mm,
referencing this item, yet still
whichever you prefer. Examples:
allow current product to be
submitted.
Concrete to be 200 mm thick. (0.2 m
could be used)
Rounding
Clearance shall be 1500 mm.
(1.5 m
Having seen many metric drawings,
could be used)
and seeing the downstream effect, we
feel rounding of design dimensions
This practice differs from drawing
is a very high priority.
usage where mm are used exclusively in
many areas.
Too many review comments on metric
projects state that we do not prefer
In specifications, the unit (ex, m or
bar spacings at 305 mm on center, or
mm) is almost always present. Little
base plate dimensions of 460 x 460,
room exists for confusion. On drawings,
and similar items.
using mm eliminates the need to write m
or mm, and eliminates decimal usage for
The professional rounding concept
all but large scale civil and road
helped, but we have developed a
design drawings.
simpler, but firmer stance on this
issue.
Centimeters should not be used. A small
class of items reference standards
The Rachet:
100
50
10
5
1
using cm or cm2, such as fire ratings
for some products. These areas only,
The rachet is a five level priority
which account for less than 2 % of
system, 100 being highest priority,
specification references, should make
which requires justification to move
reference to cm or cm2.
down one rachet. (ex, to move from
100 to 50)
It is recommended that each region
establish a directory of pure SI
Thus design dimensions, created in
specifications, as we have done, and
ones mind, should be increments of
not mix SI and english specifications.
100 mm, unless solid reasons exist
to move down a rachet to design in
It is also not recommended to have both
50 mm increments.
metric and english in a guide
specification section, as this requires
Room sizes in new construction and
spec writers to edit english out of the
renovation are ofcourse in 600 mm
document.
increments unless not possible.
Nominal Technique Many spec references
The rachet applies most directly to
can effectively use nominal mass,
design dimensions, which are smaller
nominal volume, or nominal length
than room dimensions, such as 3600 x
technique. Ex, if 1 gallon of product x
4800, but larger than product
is required (or, 3.785 L) the spec
dimensions, such as
could be rewritten using nominal
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