KQL syntax for serial difference/delta filter

thanks..then how do we put a filter in watcher JSON to get only those docs where "delta" is greater than particular value...

for example ,
value 1: 50, doc:1
value2 : 50, doc:2
value 3: 100, doc : 3 - delta : 50 ,

need to set a filter in watcher alert when delta is greater than 0