This is something Sergey had helped me with - but he must be taking Sunday off! The big thing I learned so far from Sergey was in regards to passing paramenters to UDFs as references (eg so they would return a value - see @iPart below). The demo below needs to return a parameter passed by reference (i think) to MSChart's TwipstoChartPart method. I would like to know how to determine if this method is "really" exposed to VFP - and if it is, how to make it work. If anyone knows this will not work, or could help me make it work (Windows API functions - maybe), I would be most appreciative - I would be willing to do a few hours of grunge work in exchange. What follows below are my most recent pleas to Sergey.
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Again Sergey my thanks - I was toggeling between setting UDFPARS TO VALUE and then asserting an @iPart. When the CODE breaks from a UDF PARM the environment (i think) has to be cleared.

Any whoo - I got it to bite with an @iPart designation once, and it failed on the Index1 parameter that did not have the '@'. Before that the whole TwipstoChartPart threw an 80020005 (type) error. It was a good feeling (for about 6 seconds) And then as my hacks usually go - without saving a copy with the successful @iPart fire (it was pretty cluttered by that time) I went in and instead of editing ONE thing - I got creative and messed with 2 or three - before I even knew why it worked - and then forgot the [apparent] working hack (I had to mow the lawn today). And then I tried (in vain) to make it happen for 5 hours to no avail. I don't know if the success was because a previous TYPE error had busted the environment (a false success) or because @iPart was .F. or a Zero - or a local paramter. When VB SETs a variable as an integer, is it initialized as a Zero - or as an .F., like VFP? When I (think) had success - the Parameters were local to the mouse move. I moved them to public - but left commented LOCAL declaration in mouse move,

Anyway heres a cleaned up test bed. The form chart program (TWIPPER.PRG) and a script to reset the environment (RS.PRG). The caption of the form echos mouse move pixels and mouse move twips to pixel - and on the most right of the caption the iPari is suppose to echo. It works as posted - put iPart is always zero.

Take a look if you can and tell me where I am screwing up - I'll send a bubble/fan dancer to your dwelling for Valentines Day!!!

* Twipper.PRG (terry)
SET EXACT ON
DeclareWindowsAPIFunctions()
PUBLIC myform as Form, unLTVX, unLTVY, iPart As Integer, iseries As Integer,;
      idatapoint As Integer,ix1 as integer, ix2 as integer, ix3 As Integer,;
      ix4 As Integer,lUseTwipsToPixels
STORE 0 TO iPart,iseries,idatapoint,ix1,ix2,ix3,ix4
GetDisplayMetrics()
lUseTwipsToPixels=.t. && Use Twips to pixel convertion - else - use pixels (X,Y)
myform=CREATEOBJECT('frmTwipper')
myform.show

DEFINE CLASS frmTwipper as form
height=600
width=800
autocenter=.t.
borderstyle=2
PROCEDURE release 
this.queryunload
ENDPROC 
PROCEDURE init
this.cntChart.width=this.Width
this.cntChart.Height=this.height
ENDPROC 
PROCEDURE QueryUnload
CLEAR EVENTS
ENDPROC 

PROCEDURE resize
ENDPROC 
ADD OBJECT cntChart as cntChartClass
visible=.t.
ENDDEFINE &&frmTwipper

DEFINE CLASS cntChartClass as Container
top=0
left=0
backstyle=1
backcolor=RGB(255,255,255)
borderwidth=1
procedure init
with this.ocxChart
.width=thisform.width-2
.height=thisform.height-2
.ChartType = 3 && VtChChartType2dLine
.AllowDithering = .f.
.AllowSelections = .f.
.AutoIncrement = .f.
.AllowDynamicRotation = .f.
.AllowSeriesSelection = .f.         
.COLUMNCOUNT = 1
.RowCount = 8
.Backdrop.Fill.Style= 1 && VtFillStyleBrush
   with .Backdrop.Fill.Brush.FillColor
   .red=255
   .green=255
   .blue=255
   ENDWITH &&.Backdrop.Fill.Brush.FillColor
*!* Populate the DataGrid Object.
FOR lnCol = 1 TO 1
   FOR lnRow = 1 TO 8
   .COLUMN = lnCol
   .ROW = lnRow
  .DATA = lnRow * 10
   NEXT ROW
NEXT COLUMN
*!* Use the chart as the backdrop of the legend.
.ShowLegend = .T.
.visible=.t.
ENDWITH &&this.ocxChart
ENDPROC &&Init
PROCEDURE resize
ENDPROC 
ADD OBJECT ocxChart as ocxChartClass
visible=.t.
ENDDEFINE &&cntChartClass

define class ocxChartClass as Olecontrol
OleClass="MSChart20Lib.MSChart.2"
BorderStyle=1
top=1
left=1
PROCEDURE init
ENDPROC
PROCEDURE MouseMove(Button, Shift, X, Y)
*!*	LOCAL iPart As Integer, iseries As Integer, idatapoint As Integer,;
*!*	      ix1 as integer, ix2 as integer, ix3 As Integer, ix4 As Integer
*!*	STORE 0 TO iPart,iseries,idatapoint,ix1,ix2,ix3,ix4
lnX=IIF(lUseTwipsToPixels,x*unLTVX,x)
lnY=IIF(lUseTwipsToPixels,y*unLTVY,x)
*!*	this.object.SelectPart(4, 0, 0, 0, 0)
this.object.TwipsToChartPart( lnX, lnY, iPart, ix1, ix2, ix3, ix4)
thisform.caption=PROGRAM(0)+[ - Pixels: ]+TRANSFORM(x)+[, ]+TRANSFORM(y);
                           +[ - Twips : ]+TRANSFORM(x*unLTVX)+[, ]+TRANSFORM(y*unLTVY);
                           +[ - TwipsToChartPart : ]+TRANSFORM(iPart)
ENDPROC 
ENDDEFINE &&ocxChartClass

PROCEDURE DeclareWindowsAPIFunctions()
declare integer GetActiveWindow in WIN32API
declare integer GetDC in WIN32API integer iHDC
declare integer GetDeviceCaps in WIN32API integer iHDC,integer iIndex
ENDPROC &&R6_PSA_DeclareWindowsAPIFunctions

procedure GetDisplayMetrics()
local liHwnd,liHDC,liPixelsPerInchX,liPixelsPerInchY
liHwnd=GetActiveWindow()
liHDC=GetDC(liHwnd)
* Pixels per Inch
liPixelsPerInchX=GetDeviceCaps(liHDC,88)
liPixelsPerInchY=GetDeviceCaps(liHDC,90)
* Twips per pixel and store
unLTVX=1440/liPixelsPerInchX
unLTVY=1440/liPixelsPerInchY
ENDPROC &&GetDisplayMetrics()
* END OF TWIPPER.PRG

And below is the cleaner script

* RS (RS.PRG) ReSet environment
* When the program breaks on a UDFPARMS error 
* Type DO RS in command window to clear beforw
* edit and and re-test. 
use
clear all
close all
rele all
on error
* END OF RS.PRG

Lucy you - huh - if you have a minute - I would appreciate it - even if I have to learn that the TwipstoChartPart method cannot be properly exposed in VFP. Being Mr. POY (again) is a heavy cross to bare!

Thanks Sergey!