Rain "Year to Date" and "Month to Date" Differential Script

Internet Custom Templates and Scripts
10

It looks like the tags are in and working:http://www.cavecountryweather.com/index.php
Couple of questions:

  1. How to add the + and - symbols?
  2. I am not quite sure where the value "YTD Differential: 16.66 in " came from and is it + or - ?
 <tr>
                <td class="data1">MTD Differential: </td>
                <td style="text-align: right;" class="data1">
				  
                  <?php echo $avg_mtd_rain . $uomRain; ?>
                </td>