How is data logger data downloaded?

Plug the base unit in using the AC adaptor. Insert USB stick/flash drive into unit’s USB port. Wait until it beeps. Remove USB stick/flash drive (the data will be available in a .CSV file on the USB stick/flash drive). Video instructions can be found here.

Does the TM-4127 log data?

No. However, it does show high/low readings and meanwhile alarms can be set to signal out of range conditions.