The data recorded to a sensor’s MicroSD card reflects data averaged across two minutes. If a sensor is connected to WiFi, this is also the same data that’s sent to the PurpleAir Map and shown as real-time averages.
The occasional gap you noticed is fully explained in our Why is there a gap in the SD card data article. This is due to a soft reboot of the device which can’t be disabled.
Feel free to let us know if you have further questions.