So lets say I put in $100 dollars. I buy while its at a low of $10,400. The price goes up to $10,400 and I sell. Whata my profit?
To determine if you are already earn profit it is better that you know what is your starting value. Like what you said, you buy that coin for just $10,400 so if wanted to know that you already gain you need to sell that coin in much higher value than $10,400 so supposed to be it should be $10,500 and up therefore you can earn to that by $100 and up. It is much better if you patiently wait for the right to sell it when it will be double or triple or maybe much more than that so you can able to gain much higher profit.
If you invest $10,400 and sell it higher than your investment you can gain profit with your investment but if you sell it lower than your investment you gain nothing and losing your investment. It is very simple strategy mate to calculate with your profit. Just look like this output(investment sold) minus input (investment) $11,000 - $10,400 = $600 or 5.8% your profit with your investment.