Calc: How to create a simple "Goal Seek"-macro?

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I tried to create a simple macro to run a "Goal Seek" (same as "Tools" -> "Goal Seek...").

Let's assume the following situation:

• Formula cell is A1
• Target value is in A2
• Variable cell is A3

I recorded a macro that contains the following code:

REM  *****  BASIC  *****


sub Goalseek
rem ----------------------------------------------------------------------
rem define variables
dim document   as object
dim dispatcher as object
rem ----------------------------------------------------------------------
rem get access to the document
document   = ThisComponent.CurrentController.Frame
dispatcher = createUnoService("com.sun.star.frame.DispatchHelper")

rem ----------------------------------------------------------------------
rem dispatcher.executeDispatch(document, ".uno:GoalSeekDialog", "", 0, Array())

rem ----------------------------------------------------------------------
dispatcher.executeDispatch(document, ".uno:GoalSeek", "", 0, Array())


end sub

Unfortunately, nothing happens if I run the macro by hand. How can I adopt it to the upper cell names and make it work?