Wigginton collaborated with Wozniak on the circuit design and ROM software for the Apple II in 1977. As Wozniak wired up color graphics circuitry, Wigginton wrote machine language graphics subroutines, and Chris Espinosa, another high school student, wrote demo programs in BASIC. Wigginton wrote several early programs for the Apple II, including a checkbook-balancing program co-authored with Apple's vice-president of Marketing Mike Markkula. Wigginton was one of the Apple employees who adapted Microsoft's 6502 BASIC for the Apple II; it was dubbed Applesoft BASIC. The "Applesoft BASIC Reference Manual" includes a section entitled "Rounding can be Curious", in which it is documented that the ROUND function, which rounds a number to a prescribed accuracy, is not monotonic: in other words, for some "x" and "y", such that "x"<"y", ROUND("x")> ROUND("y"). (The problematic ROUND function does not appear in Applesoft II, the version that most Apple II users are familiar with.)