In Pokémon Diamond and Pearl, as part of the Hearthome Gym's puzzle, the player is asked to calculate some basic mathematical questions. In Pokémon Brilliant Diamond and Shining Pearl, it is always based on National Pokédex number. In Pokémon Diamond, Pearl, and Platinum, this is based on Sinnoh Pokédex number at first, but changes to National Pokédex once the player obtains the National Pokédex. When an answer is displayed, if the player has a Pokémon registered as "Seen" in their Pokédex whose Pokédex number is equal to the result (rounded down to the nearest integer), the calculator will play that Pokémon's cry. In Pokémon Brilliant Diamond and Shining Pearl, it has been reported to exhibit wonky behavior. In Pokémon Brilliant Diamond and Shining Pearl, decimal digits are truncated in the same way for the display, but the truncated digits remain in number itself and continue to be used in future calculations using that number. In Pokémon Diamond, Pearl, and Platinum, if a calculation results in a number that would require more than 10 characters to display, decimal digits are truncated until the number fits in the display (with the truncated digits discarded from the actual number, not just the display) if there are more than 10 digits in the integer part of the calculated number, a sequence of question marks are displayed instead of the number. The calculator can only display up to 10 characters in the number: For integers it can display up to 10 digits, but for non-integers it can only display up to 9 digits due to the decimal point occupying one of the displays. The Calculator (Japanese: けいさんき Calculator) is a basic calculator app that includes addition, subtraction, multiplication, and division. It's perfect for figuring out math questions that might pop up." "The Calculator can handle up to ten digits. In Platinum, the apps are ordered in the same order as they are on the Pokétch in Diamond and Pearl.
Listed in each section below is the in-game description of its app, followed by its in-game location and further information about it. The rest are not available at the start but can be received at a later time, and a few must be obtained by showing a certain species of Pokémon to another character. In Diamond and Pearl, there are 25 available apps, four of which are included with the Pokétch. The user scrolls through a Pokétch's apps by tapping a button on the side of its screen. The Pokétch Company, as well as independent developers, periodically create new apps. The Pokétch's functionality comes from the applications, or Pokétch apps, that are installed in it, making it extensible.