Simple Mathematical Rounding shall not be used.
Having seen many metric drawings, and seeing the
Ex, A design dimension simply converted to 3658 mm.
downstream effect, we feel rounding of design
dimensions is a very high priority.
Professional Rounding shown below, takes simple
Too many review comments on metric projects state that
mathematical rounding, adds professional judgment.
we do not prefer bar spacings at 305 mm on center, or
base plate dimensions of 460 x 460, and similar items.
Step 1. Convert The Dimension Mathematically
A pavement width in some codes becomes 914 mm.
The professional rounding concept helped, but we have
developed a simpler, but firmer stance on this issue.
Step 2. Select A Replacement Dimension (Use Rachet)
1000 would be the preferred replacement.
The Rachet: 100 50 10 5 1
900 would offend the code and could not be used.
The rachet is a five level priority system, 100 being
For non code dimensions, smaller dimensions in
down one rachet. (ex, to move from 100 to 50)
increments of 100 might be selected.
Thus design dimensions, created in ones mind, should be
Ex, custom cabinets are to be built to a width that
increments of 100 mm, unless solid reasons exist to
converts to 508 mm. 500 would be the probable choice,
move down a rachet to design in 50 mm increments.
and would be permitted if this were not a code or exact
Room sizes in new construction and renovation are
ofcourse in 600 mm increments unless not possible.
The rachet applies most directly to design dimensions,
which are smaller than room dimensions, such as 3600
x 4800, but larger than product dimensions, such as
92 mm metal stud sizes, which are often fixed.
Examples: bathroom stall widths, bathroom component
mounting heights, concrete wall thickness, window
dimensions, base plate sizes, parking stall widths,
cabinet widths, counter heights, slab thickness, door
louver and window sizes, ductwork sizes, shelf spacing,
railing heights and on center dimensions, landscape
installation dimensions, etc.
Critics have indicated this is not always possible, which
we know. But increments of 100 and 50 mm should now
become the baseline for project design, with 10 and 5
mm increments used only as required.