Pocket Chrono is not included
This chronometer mount by FX for the Pocket Chrono can be mounted on the side accessory rails of your Impact or Maverick, after which the Pocket Chrono can be attached to it, instead of to the barrel. This prevents unwanted alterations to the point of impact of pellets, as tends to happen when the extra weight of the Pocket Chrono is attached to the barrel.
The FX Pocket Chrono chronometer mount is largely made of carbon fibre, weighing only 90 grams, and barely adds any weight to your setup.