As You all know that you can earn by upvote.
but they are not unlimited . there is actually a limit,
you Start With 100% vote power. As you vote your 2% voting power Decrease. means for 1 upvote you will use up 2% of your votingpower.
Each Day you Regenerate 20% voting power. Means If you used your all Voting Power . It will take 5 days to get it up to 100%.
The Lower your Voting power is the less Weight your vote carry so the lower the reward.
How to Check VotingPower.?
Go to https://steemdb.com/@username
https://steemd.com/@username
on the left side you will see your voting Power.