Thanks, but I'm looking for information about using a Westcott Digital
Calibration Target to set correct white balance when shooting a high key
set.

The procedure you describe above is for color correction after you've shot a
scene using incorrect white balance.  While that procedure can remove minor
unintended color tinges, it doesn't really restore white balance.  For
example if you shoot a blue blouse on a white background using a digital
camera with an incorrect color temperature setting, the white background
won't come out looking quite white.  If you then "correct" the white
background using the Curves tool in Photoshop, you unfortunately also change
the color of the blue blouse.  If someone then buys a blouse based upon your
picture they will be disappointed to discover that the product color doesn't
match the pictured color.

A high key set is one in which the white background is deliberately
over-exposed to the extent that it becomes indiscernible in the photo.  The
subject is lit separately, and correctly exposed.  When shooting a high key
set with a digital camera, if you don't set the exposure and white balance
correctly, bands of grayish-blue or pinkish-red color appear in the digital
image.  Correcting those bands without altering the exposure or white
balance of the subject can be difficult, often requiring matt work.

I've heard from several sources that the Westcott Digital Calibration Target
is very helpful in setting the correct exposure and color balance.  But
there's some trick to it; it's not done in quite the same way as setting
white balance off an 18% gray card, from what I've heard.

Can someone who has used the Westcott Digital Calibration Target for high
key photography please explain the technique?  Thank you in advance.