It is expected that most devices will send more than one variable at a certain time. And when visualizing the data, the user may want to see them synchronized at each sample period.
For example, a device sends a GPS location, speed and voltage variables at certain frequency. If they are acquired and sent with exactly the same time stamp the user can visualize the 3 variables together at each time sample. However, if there is any delay between them (time stamps of the three variables not matching exactly), the system will not be able to group them correctly ‘by time’.
That is when the field ‘group’ in the JSON comes to help. A batch of acquired variables can be synced by adding the same ‘group’ in their samples. For example, the first acquisition could be: GPS location, speed, and voltage variables all with group = 0001, the second acquisition would have group = 0002, and so on. When visualizing these batches of data combined in a Table or Map for example, just select the option ‘Group by group’.
To learn how to add the ‘group’ in the JSON, check out the API documentation.