If you have one of the Honeywell range of Humidity sensors, these give a 1-4V signal, to convert this into proper RH to display on a Gateway screen (or use in a calculation) use the following value convert:
 

   <eventInterface module='EventHandlers.ValueConvert' name='ValueConvert'>
       <eventtype type=''>
          <eventsource source='webbrick/1/AI/1'>
               <event>
                   <newEvent type='internal' source='insideHumidity' preoffset='16' multiplier='1.54'>
                       <copy_other_data val="newVal"/>
                   </newEvent>
               </event>
           </eventsource>
       </eventtype>