# Kibana JSON input calc fields **URL:** \ **Category:** Kibana\ **Created:** [April 10, 2020, 12:39pm UTC](https://discuss.elastic.co/t/kibana-json-input-calc-fields/227501 "2020-04-10T12:39:27Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![Robin020](https://avatars.discourse-cdn.com/v4/letter/r/71c47a/32.png) [@Robin020](https://discuss.elastic.co/u/Robin020)\ **Post date:** [April 10, 2020, 12:39pm UTC](https://discuss.elastic.co/t/kibana-json-input-calc-fields/227501/1 "2020-04-10T12:39:27Z")
Hi, I use heartbeat for monitoring some url's. But unfortunately the resolving of my VPS is slow. So I would like to exclude the `resolve.rtt.us` field in a visualization. In the visualization I use the `monitor.duration.us` field on the Y as. I try to do this calculation: `monitor.duration.us` - `resolve.rtt.us`. `{"script" : "doc['monitor.duration.us'].value - doc['resolve.rtt.us'].value"}` Above JSON input doesn't work. Could somebody help me with this? Best regards, Robin ---
**Author:** ![Larry\_Gregory](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/larry_gregory/32/34969_2.png) [@Larry\_Gregory](https://discuss.elastic.co/u/Larry_Gregory)\ **Post date:** [April 10, 2020, 1:05pm UTC](https://discuss.elastic.co/t/kibana-json-input-calc-fields/227501/2 "2020-04-10T13:05:21Z")
Hi @Robin020, > [@Robin020](#): > > Above JSON input doesn't work. Could somebody help me with this? Do you get a specific error message? Can you show me exactly where and how you're trying to use this script? ---
**Author:** ![system](https://us1.discourse-cdn.com/elastic/original/3X/1/a/1ac57faf039f6b580b3f104ef42a2a89e41014de.png) [@system](https://discuss.elastic.co/u/system)\ **Post date:** [May 8, 2020, 1:05pm UTC](https://discuss.elastic.co/t/kibana-json-input-calc-fields/227501/3 "2020-05-08T13:05:33Z")
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