The Up/Down Counter increases the counter whenever the Increment input receives a rising edge and it decrements the counter whenever the Decrement input receives a rising edge.
If the Reboot survive property of the node is enabled, the counter value is persistent which it means that it doesn't get lost when the server reboots and after the reboot, the counter increment/decrement the last saved value; otherwise, the counter value gets resetted every time the server reboots.
The Start Date output connector sends the last date and time the counter received a Reset signal. When the Reset input receives 1, the counter gets resetted, Output goes to 0 and Start Date is updated; the counting will start again only after Reset goes back to 0.

 Behaviour of Up/Down Counter

Behaviour of Up/Down Counter