# Revision history [back]

Several variables are already registered by default, so you don't need to register them, you just need to create the appropriate filters as in the watcher program (so skip the introspectable_plugin part).

The URI for joint velocity should be something like this:

data://world/default/model/revolute_model/joint/revolute_joint?p=axis/<axis_number>/double/velocity

Several variables are already registered by default, so you don't need to register them, you just need to create the appropriate filters as in the watcher program (so skip the introspectable_plugin part).

The URI for joint velocity should be something like this:

data://world/default/model/revolute_model/joint/revolute_joint?p=axis/<axis_number>/double/velocitydata://world/<world_name>/model/<model_name>/joint/<joint_name>?p=axis/<axis_number>/double/velocity