# What is the CPLX button on a calculator?

On my cheap "dollar store" scientific calculator, it has a 2nd function button named "CPLX". When you press it, the calculator displays some text similar to the "DEG, RAD, GRAD" that says "CPLX". When in this mode, you can't add, subtract, multiply, or divide. The equals button doesn't even work.

What is this and how is it used? I'm wondering if maybe it's for complex numbers, seeing that there's also a "a" and a "b" button next to it.

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This is for complex numbers, ones of the form $a+bi$ where $a,b$ are real and $i$ satisfies $i^2 = -1$.
More correctly $i$ is such that $i^2 = -1$ –  user88595 Oct 22 '13 at 18:08
@DantheMan here is a brief summary in Russian if it helps (1okey.ru/privat/instruction/instruction/…). They do agree that CPLX means a register of complex numbers... –  gt6989b Dec 30 '13 at 16:54