Deadreckoning div by zero

[CourchesneA]

When running the exercises workflow in the simulator we get a division by zero in the deadreckoning node:

[ERROR] [1607369074.967796]: bad callback: <bound method DTSubscriber._monitored_callback of <duckietown.dtros.dtsubscriber.DTSubscriber object at 0x7fa52ed23d60>>
Traceback (most recent call last):
  File "/opt/ros/noetic/lib/python3/dist-packages/rospy/topics.py", line 750, in _invoke_callback
    cb(msg)
  File "/code/catkin_ws/src/dt-ros-commons/packages/duckietown/include/duckietown/dtros/dtsubscriber.py", line 131, in _monitored_callback
    out = self._user_callback(*args, **kwargs)
  File "/opt/ros/noetic/lib/python3/dist-packages/message_filters/__init__.py", line 76, in callback
    self.signalMessage(msg)
  File "/opt/ros/noetic/lib/python3/dist-packages/message_filters/__init__.py", line 58, in signalMessage
    cb(*(msg + args))
  File "/opt/ros/noetic/lib/python3/dist-packages/message_filters/__init__.py", line 330, in add
    self.signalMessage(*msgs)
  File "/opt/ros/noetic/lib/python3/dist-packages/message_filters/__init__.py", line 58, in signalMessage
    cb(*(msg + args))
  File "/code/catkin_ws/src/dt-core/packages/deadreckoning/src/deadreckoning_node.py", line 136, in cb_ts_encoders
    self.tv = distance / dt
ZeroDivisionError: float division by zero

[liampaull]

what is this deadreckoning node?