Made the change but still confused. Also read the doc you sent but too dense to figure out what it means in reference to my confusion 
With vars specified still looks like ‘sd’ is still sampled. If I understand correctly only mu should be sampled? Or does the step argument in my case mean that ‘mu’ is sampled first?
Below is the graph from the notebook where I’m seeing 2 chains for both mu and sd leading to my confusion
Thank you for the help
