I use some script to change main gateweay.

:local PingStatus \
(([/ping $pingTo1 interface=$InterfaceName size=28 interval=0.5 count=$pingCount routing-table=$InterfaceName] + \
[/ping $pingTo2 interface=$InterfaceName size=28 interval=0.5 count=$pingCount routing-table=$InterfaceName] ) / ($pingCount * 2) * 100);

Sometimes variable PingStatus equal 0. I have only two variable status: $PingCount*2 (without ping lost) or zero (where all ping lost). I check my router by ping from internet. In time i have pingStatus=0 i have no packet lost from outer ping. What it can be?