API Rate Limit by ??? | ThingSpeak API | Forum

According to the API documentation "The open service via ThingSpeak.com has a rate limit of an update every 15 seconds.", but to what does this rate limit apply? Does it apply per account, per channel or per field?

For example, say I have a channel for temperatures with 4 fields mapped to 4 thermal probes. Each hour I kick off a process to update ThingSpeak. For simplicity I would prefer that my application update a ThingSpeak field as data becomes available from the corresponding probe rather than wait for all probes related to the channel to return their data. Can I update my channel with 4 separate POST requests (1 per field) in less than 15 seconds? or…

Do I need to wait 15 seconds between POSTs to each field?
Do I need group all 4 sensor readings into a single POST request?
Are my assumptions correct or should separate sensors really be on separate channels etc…

Thanks,
willnue