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Hi, the @minnowbooster account hasn't really voted today and when it does you will receive a prorata share of the revenue, but the account has so much delegation that your 150 SP will get a very small prorata share. I suggest rather undelegate and register yourself as a bot or create another account and delegate to it and register it to allow us to sell its vote.

You can also try find some open orders of that size on our delegation market to fill, that will give you a stable return.

yes, I got it. didn't think that way before. Open orders would do too. I don't know if being a bot is a good thing for me, as sometimes there are many errors to fix, and you get negative comments why something was not paid in time.... I think I'm not really ready for this

how to undelegate steem power? Please could you explain

It is same as delegation. Just give the SP as 0.