The "Realized Gains/Losses" displayed on the screen is the profit after subtracting the book value. For the calculation of book price, you can set Cryptact to use one of the two accounting methods, Average cost or Periodic average cost. The default setting is Periodic Average cost.
Please note that due to revisions to the law in April 2019, you need to notify your local tax authority if you choose to use Periodic average cost for calculating your PNL.
For more details on Average cost, Periodic average cost, how they affect the PNL calculation, etc, please refer to this article (Japanese only).