Just like each node can have a number of data sources (or devices), each device also has a number of measurements.
You can access the device page to see the different measurement points linked to your device and add new ones if the device allows.
The measurement page gives you all of the controls you need to adjust how your measurements work - you can change the name, alter the recording and disable the input all-together ( in a number of cases, you won't be using 100% of the IO available in your unit - it's always best to disable the measurement channels you aren't planning on using).
From the same page you can manage your alerts from the alert list.
Most of our intergrated devices have a fixed number of inputs and outputs which were added for you when you first added the device to rAware. As such, these devices won't allow you to add any new measurements.
The ability to add custom measurements is an advanced feature that is only unlocked by optrix support for special cases - normally when communicating directly with a PLC rather than an I/O unit.