This code works:

**************************************************
*-- Form:         form1 (c:\eltest20\test.scx)
*-- ParentClass:  form
*-- BaseClass:    form
*-- Time Stamp:   01/09/05 02:45:06 PM
*
DEFINE CLASS form1 AS form


	DoCreate = .T.
	Caption = "Form1"
	Name = "Form1"


	ADD OBJECT text1 AS textbox WITH ;
		Value = (""), ;
		Height = 23, ;
		InputMask = "##:##:##", ;
		Left = 11, ;
		Top = 26, ;
		Width = 100, ;
		Name = "Text1"


	ADD OBJECT text2 AS textbox WITH ;
		Value = (""), ;
		Height = 23, ;
		InputMask = "##:##:##", ;
		Left = 14, ;
		Top = 67, ;
		Width = 100, ;
		Name = "Text2"


	ADD OBJECT text3 AS textbox WITH ;
		Value = (""), ;
		Height = 23, ;
		InputMask = "##:##:##", ;
		Left = 10, ;
		Top = 100, ;
		Width = 100, ;
		Name = "Text3"


	ADD OBJECT text4 AS textbox WITH ;
		Height = 23, ;
		Left = 29, ;
		Top = 150, ;
		Width = 100, ;
		Name = "Text4"


	PROCEDURE addtime
		LPARAMETERS nSecs, nSec2
		LOCAL c_hours, c_min, nLocSec
		IF TYPE("nSecs") # "C" .OR.;
		   TYPE("nSec2") # "C" .OR.;
		   TYPE("nSecs") # TYPE("nSec2")
		   RETURN ""
		ENDIF
		nLocSecs = VAL(LEFT(nSec2,2))*3600
		nLocSecs = nLocSecs + VAL(SUBSTR(nSec2,4,2))*60+ VAL(SUBSTR(nSec2,7,2))
		nLocSecs = nLocSecs + (VAL(LEFT(nSecs,2))*3600 + VAL(SUBSTR(nSecs,4,2))*60+ VAL(SUBSTR(nSecs,7,2)))

		nSecs   = ABS(nLocSecs)
		c_hours = INT(nSecs/3600)
		*IF c_hours > 24
		*   RETURN ""
		*ENDIF
		nSecs   = nSecs - (c_hours*3600)
		c_hours = IIF(c_hours<10,"0","")+ALLTRIM(STR(c_hours,15))
		c_min   = INT(nSecs/60)
		nSecs   = nSecs - (c_min*60)
		c_min   = IIF(c_min<10,"0","") + ALLTRIM(STR(c_min,15))
		nSecs   = IIF(nSecs<10,"0","") + ALLTRIM(STR(nSecs,10))
		RETURN c_hours+":"+c_min+":"+nSecs
	ENDPROC


	PROCEDURE text1.InteractiveChange
		thisform.Text4.Value = thisform.AddTime(thisform.AddTime(this.Value, thisform.Text2.Value), thisform.text3.Value)
	ENDPROC


	PROCEDURE text2.InteractiveChange
		thisform.Text4.Value = thisform.AddTime(thisform.AddTime(this.Value, thisform.Text1.Value), thisform.text3.Value)
	ENDPROC


	PROCEDURE text3.InteractiveChange
		thisform.Text4.Value = thisform.AddTime(thisform.AddTime(this.Value, thisform.Text2.Value), thisform.text1.Value)
	ENDPROC


ENDDEFINE
*
*-- EndDefine: form1
**************************************************

.Signature { margin-top: 12px; color: #666666; } .Signature a { color: #666666; }