What is the main problem with punch-card voting devices?
Hanging and fat chads?
It seems that the punch-card voting devices do not reliably punch clean holes in the card, resulting in:
Hanging chads: fragments of card still attached.
Fat chads: a depression where a hole was intended.
These cause the automated vote counting machines to not count the intended vote.
This caused immense controversy and delay in Florida in the 2000 US presidential election, where the vote was very close. As a result, the use of punch-card voting devices was abandoned in the US for all elections after 2000.