Calculating Error Rate

I need to monitor the Error Rate on Alvarion subscriber units. I am currently using Cacti with a custom script to monitor these units. Here is the perl script used currently to calculate the Error Rate:

     
      #!/usr/bin/perl

      # Calculate Error Rate for Breeze Access II SU - Return as percent value

      $ip = $ARGV[0];

      $cs = $ARGV[1];

      $oid_trans = '.1.3.6.1.4.1.710.3.3.8.2.3.1.0';

      $oid_retrans = '.1.3.6.1.4.1.710.3.3.8.2.3.15.0';

      $trans = `/usr/bin/snmpget -v 1 -OQv  -c $cs $ip $oid_trans`;

      $retrans = `/usr/bin/snmpget -v 1 -OQv  -c $cs $ip $oid_retrans`;

      $totalframes = $trans+$retrans
      #print "Trans: $trans";

      #print "ReTrans: $retrans";

      #print "Total: $totalframes\n"; 

      $ep = ($retrans/$totalframes)*100;

      #print "Err \%: $ep\n";printf("%.2f",$ep)."\n";
      exit;

To try and duplicate the value I have created a monitor using the Add Bulk page. The monitor name is ErrorRate, interval is set to 1 and the unit is %. The OID is:

   
     (.1.3.6.1.4.1.710.3.3.8.2.3.15.0/(.1.3.6.1.4.1.710.3.3.8.2.3.15.0+.1.3.6.1.4.1.710.3.3.8.2.3.1.0))

I also setup monitors on the two individual values. When I apply this monitor to my device it always calculates the error rate to be 0 or 1. If I pull the values from the individual OID monitors and calculate the values by hand it seems to be around 50% error rate. The actual ErrorRate on the device is around 24%.

I'm currenlty using the free OpManager(8030) for evaluation purposes. If I can get these monitors to work we'll upgrade to a professional version.

I'm not sure what I'm doing wrong. Any suggestions or feedback would be greatly appreciated.

Thanks,

- Todd

PS - I'd really also like to be able to do a real time graphs on these monitors as well. Something similar to the realtime interface graphs.