I've only been a BullCharts user for about 3 or 4 weeks, so this probably isn't the most mindblowing bullscript you've ever seen, but it should do the trick...

[name="Trading Range Scan"]
[author="investforwealth"]

[citation="BullCharts Forum:  http://www.bullchart.com.au/Forum/forum_posts.asp?TID=421 in response to a request by Vito 24/05/2007"]

[description="This scan calculates the trading range for the current day and compares it to the trading range for the previous day. It returns any security where the current day's range is less than 51% of the previous day's range"]

{Setup Ranges and Run Filter}

RangeToday := High - Low;
RangeYesterday := Hist(High,1) - Hist(Low,1);
RangeChange:= RangeToday / RangeYesterday;
RangeChange < 0.51

[name="Today's Range"]
RangeToday;

[name="Yesterday's Range"]
RangeYesterday;

[name="Range Change"]
RangeChange;

I've attached the scan as a file for your convenience. 

2007-05-25_010305_Trading_Range.sc

It is probably more elegant to create an indicator that provides a marker and run a scan using the indicator - this allows you to use the GUI to set the percentage change you're looking for and to also easily add further scan criteria, such as a minimum volume or share price.  The indicator and the second scan are also attached, take your pick which you use. 

2007-05-25_010331_RangeDiff.bss

2007-05-25_010343_Trading_Range_2.sc

Let me know if I can be of any further help.