A mathematics learning disability. The 9th Circuit Court of Appeals used this word in their opinion postponing the gubernatorial recall election, applying it to the voiting machines themselves! C.f. dyslexia. Dyscalculia web site is here..
Here’s an excerpt from the ruling:
In this case, plaintiffs allege that the fundamental right to have votes counted in the special recall election is infringed because the pre-scored punchcard voting systems used in some California counties are intractably afflicted with technologic dyscalculia.