See:

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Note added at 9 mins (2006-06-26 21:11:23 GMT)
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The following example illustrates the application of section
10-703(c)(1)(i) in states that calculate a taxpayer's income tax
according to the income allocable to that state, i.e.., non New York-
type tax structures:
Example 1 - TP earned $100,000; of this, $60,000
was earned in Maryland, and $40,000 was earned
in State X. State X taxes the income earned
in that state at 10%. TP would pay $4,000
($40,000 * .10) of tax to State X, and this
would be the tax credit TP would be permitted
to take under section 10-703(c)(1)(i).

http://caselaw.lp.findlaw.com/data2/marylandstatecases/cosa/...