[ic] Price difference

[Aftermarket Cellular]

Hi,

I have the following code in the promo component of my store. I would like
to add a line "You Save:" with the difference between these two prices. I
tried simply subtracting these fields between calc tags, but had no luck.
Could someone please help me with this, it seems like it should be simple. I
am using 4.8.6

<tr> 
 <td align="center" colspan="2">
  <b>Sale Price: [loop-price]</b>
 </td>
</tr>
<tr> 
 <td align="center" colspan="2">
   <i>MSRP: $[loop-field price]</i>
 </td>
</tr>

Thank you
-Bill