Here is what the message data looks like for this device. (The second line may be folded over on your screen, unless you enlarge this window.)

<-PC at 5945 msec: <LF>
->PC at 5966 msec: <mt><i0 i="0"/><n0 i="573"/><i1 i="0"/><i2 i="0"/><i3 i="0"/><i4 i="0"/></mt>

The first line starts with "<-PC" to indicate that this message is going OUT from the PC to your device.  The time "at 5945 msec:" is the elapsed time in msec since we started logging data.  (If we like, we can turn off the display of time by unchecking the "Display times" checkbox on the mtDebug window.)

The content of the first message is shown after the colon: <LF> indicates just a heartbeat signal to keep the connection alive, but no data was sent from the PC this time (because we didn't click any buttons or other controls on our layout).

The second line starts with "->PC" to indicate that this message is going IN to the PC from your device. The arrival time of this message is shown, and after the colon, we see that this message contained some data.