HTML Calculated Column Indicators

Question

I'm trying to insert KPI indicators from the Out of the Box SharePoint images when my slippage column is at certain points, but the indicators don't seem to be showing, please can you help me with my formula:

=IF(Slippage>30,"/_layouts/images/ewr218l.gif",IF(AND(Slippage>=-7,Slippage<=-29),"/_layouts/images/ewr219l.gif",IF(AND(Slippage>=-7,Slippage<=29),"/_layouts/images/ewr219l.gif",IF(Slippage<7,"/_layouts/images/ewr217l.gif","/_layouts/images/ewr217l.gif"))))&";'>"

Answer 1

="<DIV><img src='"&IF(OR(Slippage>30,Slippage<-30),"/_layouts/images/ewr218l.gif", /* s>30 or s<-30 */
   IF( OR( AND(Slippage<=-7,Slippage>=-29),AND(Slippage>=7,Slippage<=29)),
     "/_layouts/images/ewr219l.gif",  /* true, thus -29<=s<=-7 or 7<=s<=29 */
     "/_layouts/images/ewr217l.gif"   /* false, thus -7<s<7 */  
   )
 )&"'></DIV>"

(remove comments /* */, spaces and linebreaks before pasting)
see also: http://www.sharepointoverflow.com/questions/7256/html-calculated-column-formula