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You can give out as many steem upvotes as you like per day. If you have less than about 500 STEEM POWER, each vote will use up 2% of your remaining voting power, and the actual $ rewards received by authors will decrease. You can see your voting power at https://steemd.com/@myatthu.myatthu
Your voting power recovers 20% in 24 hours, or 0.83% per hour.

Thank you for your answer. But now I have 43% voting power and I vote your comment but why no reward?

Probably because right now your STEEM POWER is quite small, and the price of STEEM has taken a big drop (along with most other cryptos), so your 43% vote is worth less than USD 0.01. I think there is still a reward, its just too small to show in USD

Thank you so much for knowledge sharing. I know well now.😘