[amibroker] Scaling into a position based on an indicator

[droskill]

Let's say that I've got an indicator.  And I'm trying to scale into
positions as that indicator drops from 20 to 15 to 5.

I want to buy initially below 20, and then scale in again if the
indicator breaks 15, 10 and 5.  Here's the code I have so far:

Buy = IIf(BuySignal1 OR BuySignal2 OR BuySignal3,sigScaleIn,0);

>From this, I get the following:

Day 1 - the indicator is at 25.
Day 2 - the indicator is at 19.
Day 3 - Buy the open.  Indicator is at 17.
Day 4 - ScaleIn position.  Indicator is at 14.
Day 5 - ScaleIn position. Indicator is at 40.
Day 6 - Exit trade.

Now, what I wanted to do is a bit different.  I'll pick it up at Day 3
(this is my simulation of what I'm trying to do):

Day 3 - Buy the open.  Indicator is at 17.
Day 4 - No buy until it breaks the next level (15).  Indicator is at 14.
Day 5 - ScaleIn position.  Indicator is at 30.
Day 6 - Exit trade.

Can anyone explain how I would do this?  

Any help greatly appreciated.