QUESTION: Repeat mouseDown event while mouse button is down

I have a SpeedButton and I want to update a value in a TStringGrid
when user push left mouse button on it. Ok... this is simple ;-)
 I write SpeedButton OnMouseDown event.
But I want to update continuously this value while user push left
mouse button and stop update when user release the button.

De Bodt Lieven told me to try with THREAD:

>What about starting a thread in the onmousedown event and terminating the
>thread in the onmouseup event.
>Kind regards,
>De Bodt Lieven

How can I do this?
THANKS a lot :-)