Value on your books?, that is unless it is fully depreciated.
What a reseller would pay you for it (probably not much)?
What you could claim in tax deductions, I would suggest the Bill Clinton inflated value model
In all seriousness, we don't use the donation of equipment, especially computers and officer furniture as Investment Test credit just because it usually is of little value --
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Societies that do not find work in and of itself "pleasing to God and requisite to Man," tend to be highly corrupt.