Pies

When selling a section of your pie to buy another stock. Your invest amount changes but is false. For example.

you buy 4 stocks 100 pound in each. So you’ve invested 400. One stock doubles so makes you 100. The other 3 are equal. So you total pot is 500 with 100 profit.

If you sell the stock with profit to buy another stock with the full amount.

Your investment amount changes to 500, even tho 100 is profit in the pie. If you keep doing this you loose track of how much profit your in.

is there anyway to track this or am I just been an idiot and getting confused.

TIA