PlaceholderAPI Support
Use %speedometer_speed% to show a players speed in a scoreboard or anywhere PlaceholderAPI is supported.

If you do not wish to show the speed in the actionbar and make use of PAPI, I recommend using this config:

Code (YAML):

# Whether all players should have the speedometer enabled by default
enabled-by-default : true
# Whether players should be allowed to toggle the speedometer
allow-toggle : false
# Value between 20 and 40 is recommended
update-rate-in-ticks : 20
# Whether the speed should be shown in the players action-bar
show-in-actionbar : false
# It is assumed that PlaceholderAPI is not installed. PlaceholderAPI is not supported in any messages.
messages:
  enabled-speedometer : "&eSpeedometer is now &aenabled&e!"
  disabled-speedometer : "&eSpeedometer is now &cdisabled&e!"
  toggling-not-allowed : "&cToggling the speedometer is not allowed."
  actionbar-format : "&a%speed%"

Customizable messages
All messages are customizable. The format for how the speed is displayed in the action bar is also customizable.

Blocks per second
The units for the speedometer is Blocks Per Second. The faster the speedometer updates, the less accurate it will seem. I recommend having the update rate at something between 20 and 40 ticks (once every or every other second).