Is there an easy way to see how much was earned during the previous day? I find it hard to read those graphs.
You mean zpool's graphs? Yeah, they're hard to read.
Here's what you should do: check your "Total Earned" figure at the same time each day.
Subtract current "Total Earned" from yesterday's "Total Earned" and you will have your 24h total earnings.
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These figures can be found at
http://zpool.ca/?address=[PASTE_YOUR_MINING_ADDRESS_HERE]
Cheers,
cinderz45