hw = intraday margin (of knowledge), exam = overnight margin

open book exam = micro futures overnight margin

closed book = full-sized (it demands a lot of margin (knowledge)) - it has to be in your head, like the money needs to be in the account

minimal study or margin is needed for completing hw - you're in problem solving mode with unlimited resources

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for those who are not familiar with the contracts,

see the margin req table: https://g.teddysc.me/4d409374d3b1571b695ff581525e2ab6

for simplicity, you can assume intraday req = 1/10 overnight req

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forgive me for make up this analogy, this is not investment or study advice :)