Every time a device updates a sensor variable, then one data-point or "dot" is created. 

For example, if you have a weather station with 4 sensor variables being updated every 10 minutes (i.e. temperature, humidity, pressure and rain), then your device will generate: 

4 dots x 60/10 updates per hour x 24 hours x 30 days = 17,280 dots per month

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