The application provides two configuration types: Game Options and Settings.

Game Options

Game Options are set up when game starts and remain unchanged throughout the game. They consist of Conditions and Rule variations.

Conditions

Solving time limit

The period of time allowed to solve a puzzle.

In Training mode time limit can be disabled by selecting None.

Pack size

Packs (play mode)

Number of packs to use: 1 or 2. For example, if 2 full packs (without Zero cards) are used, the deck contains 104 cards.

Puzzle choice (Trai­ning mode)

A solvable set is selected by generate and test method, so it may take a while until a puzzle is found, especially if the magic number is different from 24.

Auto-complete

When player enters solution, the last line is completed automatically. This increases solving time by 1.5 seconds. The option is enabled by default.

Rule variations

Magic number

Allows to increase the challenge by changing target value from 24 to a different figure in range 18 to 30.

Ace as One or Eleven (1-11)

Allow an Ace (or One, if numeric cards are used) to be treated as either 1 or 11. When entering solution, tap Ace/One card and hold until it is accepted as 11.

In particular, the rule allows to solve the all-Ace (all-One) combination: 11+11+1+1 or (11+1)*(1+1). A less obvious example: set 10 5 1 1, unsolvable under standard rules, gets two solutions after adding 1-11 rule: 11+11+10/5 and (11+1)*10/5

Use Zero card

One zero card is added to a pack. If standard playing cards are used, Zero card is represented by Joker.

If Merge is enabled, a Zero card can provide a certain convenience, for example 100/4-1, or 120/5.

Allow fractions

Accepts an intermediate result as a common fraction.

Set 8 8 3 3 (solution: 8/(3-8/3)) has been mentioned in Wikipedia. Another example: 10 5 5 2, solution 5*(5-2/10). The following solution of puzzle 7 7 5 1 needs both Fractions and 1-11 to be enabled: 7*(5-11/7).

Allow negative numbers

Allows an intermediate result to be below zero.

To be honest, the only purpose to include this option is to avoid questions why it isn't there :). It appears to us that any solution involving negative numbers can be replaced by a similar one where negative values do not appear, therefore allowing negatives only increases computation time.

Use exponentiation

Enable raising to power operation, e.g. 2^3=8.

Use Merge

Merge (or concatenation) is an operation of writing one number after another: 1#2=12 1#23=123.

Example: the only solution of puzzle 10 5 5 3 involves Merge operation: 10#5=105 105:5=21 21+3=24 (or written as an expression 105:5+3).

Merge is inapplicable, if at least one of operands is a fraction, or second operand is negative.

Merge intermediate ( Merge+ )

Allows merge if one of operands is an intermediate result.

For example, the already mentioned puzzle 10 5 1 1 has a solution 1#(10-1)+5, valid only if Merge+ is enabled.

Settings

As opposed to Game Options, Settings can be changed at any moment by selecting Change Settings from the Game Menu. Settings are grouped in Appearance and Music.

Appearance

Card set

The appearance of cards in game: Playing Cards or Numbers.

Show solution as

Sequence option makes the solution intuitive and easy to understand. In turn, Expression option provides a compact and fast way to demonstrate a solution as well as show additional solutions, if several solutions exist.

Operation signs

This feature allows you to give each sign a more intuitive look.

For example, instead of asterisk sign (*) used by default for multiplication you may chose the real multiplication sign (×). Similarly, division sign (÷) can be used instead of slash (/) for division.

Background colour

The colour used to tint the background.

Animation speed

Animation speed (Slow, Normal, Fast) or Off for no animation.

Animate in place

Turns off movement of cards during animation.

Run full screen

Start application in full-screen mode. Note that full-screen mode can be enabled or disabled at any time with Ctrl + + F.

Buttons at left

Swap left and right panels to get the buttons at left.

Sound and Music

Sound effects volume

Volume of sound effects in the range from 0 (off) to 100.

Sound and music in silent mode (iOS 10+)

Enable sound effects and music even when ringer is disabled with mute switch of the device.

Music scope

Specifies whether the music is played only during the game, only between the games, all time, or turned off.

Music volume

The volume of background music in the range from 1 to 100. As opposed to device volume keys system volume control, this sets up music volume exclusively for the application.

Enable custom music (iOS 9.3+)

Grants access to user's music file to play them in the background. This permission can also be granted or revoked using system setting Privacy - Media & Apple Music - DoDo24

Pre 9.3 releases of iOS do no require such a permission. Otherwise, if permission is not granted, the application can only play internal music, so two following items are unavailable.

Music source

If custom music is enabled, showsShow a page to select an album, artist or a play list for the background music. Play lists created automatically by iTunes are referred as smart playlists.

Shuffle music tracks

If enabled, the music tracks are played in random order, otherwise they are picked up according to the default order. Appears if severa music files are selected to play.

Show music titles

If enabled (assumed by default) the application displays each music title before playback.