Studies are ideal for training your calculation skills, because they have a unique solution and “there are no positional assessments in studies” (Botvinnik), so there is no argument if your solution is correct or not. But you need to choose the right studies. Many modern studies are unsuitable for the average player, because they are too complex, and rely on computer-generated key positions, such as reciprocal zugzwangs, etc. Many others are just too difficult for the average player to have any real hope of solving. Sadly, books such as John Nunn’s “Endgame Challenge” and Dvoretsky’s “Studies for Practical Players” are just too hard for the average player.
Instead, look out for studies by composers from the earlier part of the 20th century, especially Kubbel, the Platov Brothers, Fritz, and Troitzky. They usually have relatively few pieces on the board, and single-variation solutions that are only 6-7 moves long. These are ideal for calculation practice, and within the average player’s solving capacity. Two excellent books of such material are Jeno Ban’s “The Tactics of Endgames” and Beasley & Whitworth’s “Endgame Magic”.
Here is a typical example of the sort of study to look for: