Clamped Neuron

Clamped neurons will not change their value as a network runs, though their value can be set by the user (using the random  button, the up / down arrows, or the edit dialog).   They can be used to provide a fixed source of input to other neurons. 

Tip: Clamped nodes are often useful for the input layer of a network that will be tested in the GUI.  It is often useful to set the adjustment increment of a clamped neuron to a value that makes it easy to quickly change clamped activations using the up/down keys.

Also see clamping.