Using Maximum Material Boundary (MMB) and Least Material Boundary (LMB)
The ASME Y14.5-2009 standard specifies how both the
size and position or orientation tolerances of a datum feature are to
be used in calculating the datum MMB or LMB. Refer to "ASME Y14.5-2009
Dimensioning and Tolerancing" section 4.11.6, "Determining Size
of Datum Feature Simulators at MMB", and succeeding sections on LMB.
Figure 4-16, "Example Calculations of Maximum Material Boundary",
in the ASME standard provides examples of how the MMB boundary is calculated
for a datum feature, taking into account both the size of the datum feature
and position or orientation tolerances on the datum feature.
Following the Y14.5-2009 standard, PC-DMIS
calculates datum material boundaries as follows:
MMB
- When you specify circle-M 
on
a datum feature of size, PC-DMIS
calculates the datum MMB by including the effects of size and any
preceding position or orientation tolerances on the datum feature,
while respecting the datum order of precedence as specified in the
ASME Y14.5-2009 standard. Precedence in a FCF moves from left to right.
LMB
- When you specify circle-L 
on
a datum feature of size, PC-DMIS
calculates the datum LMB by including the effects of size and any
preceding position or orientation tolerances on the datum feature,
while respecting the datum order of precedence as specified in the
ASME Y14.5-2009 standard. Precedence in a FCF moves from left to right.
Stating a Specific Boundary
If you want to define a specific boundary, perhaps
because the implied boundary is not clear, you can use the Feature
Control Frame Editor to explicitly state the boundary by enclosing
it within brackets immediately following the applicable datum feature
reference and any modifier following that datum feature reference. This
value represents the size of the material boundary. PC-DMIS
uses it to calculate the bonus on the datum feature, disregarding any
preceding position or orientation tolerances on the datum feature:
Feature Control Frame Editor showing the MMB symbol
and the square brackets that will hold the boundary value
PC-DMIS
does not currently support the use of "BSC" or "BASIC"
as discussed in the ASME standard.