You might look on this site.

http://webhome.idirect.com/~arrowmfg/

I purchased one of these and I like it...except..
the directions are VERY vaugue. There is an email address and the guy answered me promptly. He gave more directions via email.... which I suggest you get.
PS. I emailed him after my purchase and suggested that he revise his directions... and he said he was going to. .....lownslo...