You might have downloaded a disk image file
raspbian-RT-opendatalogger1512.tar.gz (if not yet, check it out).
Firstly you have to uncompress it.
$ tar -zxvf raspbian-RT-opendatalogger1512.tar.gz
This will result in
raspbian-RT-opendatalogger1512.img. After installing the card-reader (if neccessary) you have to find the right device name.
Please double check to write the image to the right device! Use
df -h to list all your drives before and after inserting the SD-card (into the slot or card reader).
$ sudo umount /dev/sdb* $ sudo dd if=raspbian-RT-opendatalogger1512.img of=/dev/sdb bs=4M conv=fsync
Basically this is all the magic. However there is no progress bar. It might even take 10 minutes for a large image with slow USB. To watch the progress execute in an other terminal window
$ sudo watch -n 30 kill -USR1 $(pgrep '^dd$')
This will print a progress bar every 30 seconds.
When finished do a
sudo sync before removing the SD-card.