You're probably not going to have a lot of luck in the precision department printing your own targets. Get an IT8 or Hutchcolor target if your software supports it.
Here's some cheap ones: http://www.targets.coloraid.de/
I printed my own without color management and then measured (3 times and averaged) with my eye-one... such a pain in the ass... anyway, now I have my target and my reference, how do I forbid Vuescan from doing anything funky to the colours? I tried the manual but it-s absolutely not clear on this point, the interface is kinda messy and definetly need some improvements.