5ths Machine 4+

The circle never stops..‪.‬

Lucy Hudson

Designed for iPhone

    • $1.99

iPhone Screenshots


Think you know your key signatures cold? Answer this: which key has 41 sharps?

The equal temperament system is a circle with 12 positions, just like a clock. And, just like on a clock, the hands keep going around and around forever. The key signature of 41 sharps is theoretically consistent with the Western diatonic system ― learn why, and learn how to find out what key it is. The Background Information and the Quiz Tips explain the system in detail, and Chronology puts it all in perspective.

Enjoy the “Perpetual 5ths Machine Boogie” while key signatures you’ve never seen before pass by on parade. Then, buckle down and solve the Quiz questions. NOW you understand music theory the 5ths Machine way!

App Privacy

The developer, Lucy Hudson, indicated that the app’s privacy practices may include handling of data as described below. For more information, see the developer’s privacy policy.

Data Not Collected

The developer does not collect any data from this app.

Privacy practices may vary, for example, based on the features you use or your age. Learn More


  • Family Sharing

    Up to six family members can use this app with Family Sharing enabled.

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