The $600 a week number was chosen because the average American makes $900 a week, and the average unemployment amount is $300. $900 - $300 = $600 to make up the

The $600 a week number was chosen because the average American makes $900 a week, and the average unemployment amount is $300. $900 - $300 = $600 to make up the shortfall and get everyone to the average. This is obviously flawed, and the initial idea was income replacement so your income remained the same, but the state of the IT infrastructure in unemployment offices across the US is so dismal there was no way they could cope with that requirement.