Flatness - Legacy and err non legacy?

huangyhg

Flatness - Legacy and err non legacy?
Back again folks, as confused as ever.
I'm running a large aluminium cover (Should I say aluminum?) and one feature is flatness of the face. Taking 18 hits and displaying flatness. out of curiosity, as my initial reporting showed it right on max limit, I defined the plane as a datum and used non-legacy dimensioning (Dunno what it's really called) to show drawing style and it reported a totally different result. I've enclosed the code below, and it shows my legacy flatness measured at 0.100mm, what it doesn't show is that the non-legacy style gave a measured flatness of 0.079mm.
I'm confused (As always). I've checked the help files but haven't found anything to explain this to me, and I'm now concerned that one of my methods is wrong, but which one?
Can anyone explain to me where I'm going wrong, in small words of no more than two sylables please? (Only had time for one coffee this morning)
Cheers
Code:
Code:
DATUM_FACE =FEAT/PLANE,CARTESIAN,TRIANGLE
            THEO/<172.978,-80.685,2>,<0,0,1>
            ACTL/<172.981,-80.68,-1.362>,<-0.0006048,-0.002509,0.9999967>
            MEAS/PLANE,18
            HIT/BASIC,NORMAL,<2.571,35.169,2>,<0,0,1>,<2.574,35.174,-1.226>,USE THEO=YES
            HIT/BASIC,NORMAL,<2.567,-17.444,2>,<0,0,1>,<2.57,-17.44,-1.332>,USE THEO=YES
            HIT/BASIC,NORMAL,<4.442,-55.024,2>,<0,0,1>,<4.445,-55.02,-1.403>,USE THEO=YES
            HIT/BASIC,NORMAL,<15.705,-91.352,2>,<0,0,1>,<15.708,-91.346,-1.463>,USE THEO=YES
            HIT/BASIC,NORMAL,<26.344,-111.394,2>,<0,0,1>,<26.347,-111.389,-1.496>,USE THEO=YES
            HIT/BASIC,NORMAL,<54.507,-132.688,2>,<0,0,1>,<54.51,-132.682,-1.527>,USE THEO=YES
            HIT/BASIC,NORMAL,<88.93,-143.959,2>,<0,0,1>,<88.932,-143.955,-1.546>,USE THEO=YES
            HIT/BASIC,NORMAL,<127.735,-146,2>,<0,0,1>,<127.738,-145.996,-1.543>,USE THEO=YES
            HIT/BASIC,NORMAL,<159.03,-146,2>,<0,0,1>,<159.032,-145.995,-1.536>,USE THEO=YES
            HIT/BASIC,NORMAL,<192.828,-146,2>,<0,0,1>,<192.829,-145.995,-1.534>,USE THEO=YES
            HIT/BASIC,NORMAL,<229.13,-138.312,2>,<0,0,1>,<229.133,-138.306,-1.496>,USE THEO=YES
            HIT/BASIC,NORMAL,<261.678,-120.772,2>,<0,0,1>,<261.68,-120.767,-1.436>,USE THEO=YES
            HIT/BASIC,NORMAL,<287.966,-103.859,2>,<0,0,1>,<287.968,-103.854,-1.38>,USE THEO=YES
            HIT/BASIC,NORMAL,<319.262,-87.572,2>,<0,0,1>,<319.265,-87.567,-1.31>,USE THEO=YES
            HIT/BASIC,NORMAL,<334.285,-65.648,2>,<0,0,1>,<334.286,-65.647,-1.239>,USE THEO=YES
            HIT/BASIC,NORMAL,<334.288,-31.199,2>,<0,0,1>,<334.289,-31.194,-1.135>,USE THEO=YES
            HIT/BASIC,NORMAL,<335.543,11.392,2>,<0,0,1>,<335.545,11.397,-1.004>,USE THEO=YES
            HIT/BASIC,NORMAL,<336.796,38.325,2>,<0,0,1>,<336.799,38.331,-0.916>,USE THEO=YES
            ENDMEAS/
            DATDEF/FEATURE=DATUM_FACE,Z
FCFFLAT1 =FLATNESS OF DATUM_FACE
            FEATCTRLFRAME/SHOWPARAMS=YES,SHOWEXPANDED=YES
            CADGRAPH=OFF,REPORTGRAPH=OFF,TEXT=OFF,MULT=10.00,OUTPUT=BOTH,UNITS=MM
            PER UNIT=NO,
              DIMENSION/FLATNESS,0.1
              NOTE/FCFFLAT1
            FEATURES/DATUM_FACE,,
            MOVE/POINT,NORMAL,<329,-8,20>
DIM FLAT1= FLATNESS OF PLANE DATUM_FACE  UNITS=MM ,$
GRAPH=OFF  TEXT=OFF  MULT=10.00  OUTPUT=BOTH
AX    NOMINAL       +TOL       -TOL       MEAS        DEV     OUTTOL
M       0.000      0.100      0.000      0.100      0.100      0.000 -------#

huangyhg

Starting in version V4.3, Feature Control Frame (FCF) flatness uses a Tchebychev algorithm.  Legacy flatness still uses the Least Squares method.
Starting in V4.3, the FCF flatness algorithm was modified to use a min/max calculation (in conformance with both ISO 1101 and ASME Y14.5).  This generally gives a somewhat smaller flatness value than the least squares flatness.  The legacy flatness still uses the least squares flatness for all versions of PC-DMIS.  This calculation is independent of the UseISOCalculations setting.