For those who have Jeff's Ninja notes, could somehow help clarify the wording below?
The notes say for estimated tax payments, they are "required if more than $500 in tax liability is expected, or 100% current tax liability, or 100% previous tax liability." My question is (pardon for being a grammar police), if the second part is "Required if 100% of current/previous tax liability," what does that mean? 100% current liability, okay, what about it?