I have based my calibration on this article:

http://www.butzi.net/articles/vcce.htm

I use a two-tube VC head, Aristo VCL4500, but the principle is the same.

It might seem like a lot of work, but it's not bad. One session in the darkroom with a Stouffer Transmission Step Wedge and a bit of arithmetic with a spreadsheet and you're done.