# I need to perform an arithmetic operation between 2 variables of the same modbus device

**URL:** <https://discourse.nodered.org/t/i-need-to-perform-an-arithmetic-operation-between-2-variables-of-the-same-modbus-device/94258>\
**Category:** General\
**Tags:** node-red-dashboard, function-node\
**Created:** [30 December 2024 17:17 UTC](https://discourse.nodered.org/t/i-need-to-perform-an-arithmetic-operation-between-2-variables-of-the-same-modbus-device/94258 "2024-12-30T17:17:36Z")\
**Posts on this page:** 1\
**Showing post:** 3

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**Author:** ![E1cid](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/e1cid/32/77971_2.png) [@E1cid](https://discourse.nodered.org/u/E1cid)\
**Post date:** [30 December 2024 19:10 UTC](https://discourse.nodered.org/t/i-need-to-perform-an-arithmetic-operation-between-2-variables-of-the-same-modbus-device/94258/3 "2024-12-30T19:10:33Z")

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You may benefit from watching the [essentials videos](https://m.youtube.com/watch?list=PLyNBB9VCLmo1hyO-4fIZ08gqFcXBkHy-6&v=ksGeUD26Mw0&embeds_referring_euri=https%3A%2F%2Fnodered.org%2F&source_ve_path=OTY3MTQ&feature=emb_imp_woyt) they are a great source of information and will give you the basics of node-red and the uses for the standard nodes. There is also the [cookbook](https://cookbook.nodered.org/) with many examples of using the standard nodes. Take a look at `Flow conrtol` and `Create a single message from separate streams of messages`, which is an example of joining messages.

[edit] Or wire the modbus nodes in series and move each msg.payload to a new message property betwenn reads. e.g [Modbus Serial - Whole bus disconnects when one device drops - #16 by Steve-Mcl](https://discourse.nodered.org/t/modbus-serial-whole-bus-disconnects-when-one-device-drops/48555/16)

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