# How can I get the minus summary of two measurements

**URL:** <https://discourse.nodered.org/t/how-can-i-get-the-minus-summary-of-two-measurements/58364>\
**Category:** General\
**Created:** [15 February 2022 06:03 UTC](https://discourse.nodered.org/t/how-can-i-get-the-minus-summary-of-two-measurements/58364 "2022-02-15T06:03:10Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![Flixm](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/flixm/32/17122_2.png) [@Flixm](https://discourse.nodered.org/u/Flixm)\
**Post date:** [15 February 2022 06:03 UTC](https://discourse.nodered.org/t/how-can-i-get-the-minus-summary-of-two-measurements/58364/1 "2022-02-15T06:03:10Z")

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Hi,  
I need some help how I can get a negativ summary of two measurements from a photovoltaic and the consumption.

I have two different measurements 1st is the power consumption e.g. 400 watts and a second e.g. 700 watts. Now I want to calculate the minus summary of these two e.g. 400-700=300 watts.

Sorry for my English hopefully it's understandable.

All nodes I searched are for addition for Positiv results.

Thx in advance

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<div class="post-metadata">

**Author:** ![smanjunath211](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/smanjunath211/32/95742_2.png) [@smanjunath211](https://discourse.nodered.org/u/smanjunath211)\
**Post date:** [15 February 2022 07:54 UTC](https://discourse.nodered.org/t/how-can-i-get-the-minus-summary-of-two-measurements/58364/2 "2022-02-15T07:54:27Z")

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will this work?

you need `node-red-contrib-calc` contrib node

 ![image](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/4/1/4107bd1f13fbdb405f4ab08a828cdbe053de58a1.png)

```auto
[{"id":"8618330606b79d89","type":"join","z":"c0b4d8b015901a0c","name":"","mode":"custom","build":"array","property":"payload","propertyType":"msg","key":"topic","joiner":"\\n","joinerType":"str","accumulate":false,"timeout":"","count":"2","reduceRight":false,"reduceExp":"","reduceInit":"","reduceInitType":"","reduceFixup":"","x":370,"y":200,"wires":[["674c590a9310e2e4"]]},{"id":"f86265e069a42c1c","type":"inject","z":"c0b4d8b015901a0c","name":"","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"kwh","payload":"-700","payloadType":"num","x":200,"y":140,"wires":[["8618330606b79d89"]]},{"id":"460512ee9cb22580","type":"inject","z":"c0b4d8b015901a0c","name":"","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"kwh","payload":"400","payloadType":"num","x":200,"y":220,"wires":[["8618330606b79d89"]]},{"id":"674c590a9310e2e4","type":"calculator","z":"c0b4d8b015901a0c","name":"","inputMsgField":"payload","outputMsgField":"payload","operation":"sum","constant":"","round":true,"decimals":0,"x":510,"y":200,"wires":[["3f9e54561e96a04e"]]},{"id":"3f9e54561e96a04e","type":"calculator","z":"c0b4d8b015901a0c","name":"","inputMsgField":"payload","outputMsgField":"payload","operation":"abs","constant":"","round":true,"decimals":0,"x":680,"y":200,"wires":[["e471835148da203d"]]},{"id":"e471835148da203d","type":"debug","z":"c0b4d8b015901a0c","name":"","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","statusVal":"","statusType":"auto","x":850,"y":200,"wires":[]}]

```

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<div class="post-metadata">

**Author:** ![smanjunath211](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/smanjunath211/32/95742_2.png) [@smanjunath211](https://discourse.nodered.org/u/smanjunath211)\
**Post date:** [15 February 2022 08:05 UTC](https://discourse.nodered.org/t/how-can-i-get-the-minus-summary-of-two-measurements/58364/3 "2022-02-15T08:05:04Z")

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Sorry, Just realised your both inputs are `POSITIVE`, then please change the Operation in the first `calc` node to SUBTRACT, it should work.

![image](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/7/0/70877f71dbc3d5b57816613844fdd770092901df.png)

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<div class="post-metadata">

**Author:** ![Flixm](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/flixm/32/17122_2.png) [@Flixm](https://discourse.nodered.org/u/Flixm)\
**Post date:** [15 February 2022 18:24 UTC](https://discourse.nodered.org/t/how-can-i-get-the-minus-summary-of-two-measurements/58364/4 "2022-02-15T18:24:21Z")

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Thank you very much. That´s what i need

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<div class="post-metadata">

**Author:** ![system](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/1X/d073cd938eafa2e558d7c2cd59003b3ef4963033.png) [@system](https://discourse.nodered.org/u/system)\
**Post date:** [1 March 2022 18:24 UTC](https://discourse.nodered.org/t/how-can-i-get-the-minus-summary-of-two-measurements/58364/5 "2022-03-01T18:24:35Z")

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