How can I set a Shape Key value to be a driver's variable? I want a Shape Key's value to be driven by another shape key. But I don't know how to add a shape key value as a variable into a driver. I've selected single property and tried with Object or Mesh types.



Do I need to select another one?
If you use an object in the Prop field, the path to the shape key is like this:

data.shape_keys.key_blocks["Key 1"].value

If you use a mesh, you don't have to put data there, so:

shape_keys.key_blocks["Key 1"].value



And if you use the Key Prop field with your key block there, then you can just use:

key_blocks["Key 1"].value