ATAN in WPS Spreadsheet: Convert a Slope Ratio to a Principal Angle

• Introduced: documented by 2019-06-12 in the official WPS lesson; original introduction is not established.
• Availability: WPS Office for Windows Personal; no numeric release is stated in the edition metadata.
• Scope: exact current supported builds remain unverified. The Windows lesson does not establish equivalent availability in other WPS clients.
• Checked: October 14, 2026 against function-specific documentation. Examples were independently calculated; no native WPS test was performed.

=ATAN(number)

The WPS lesson describes a result between −pi/2 and pi/2. For finite real ratios, the mathematical inverse tangent approaches those endpoints without reaching them. A ratio of one is not a one-degree input.

Use DEGREES or multiply by 180/PI() after ATAN when a degree output is needed. The walkthrough contains a sentence calling its output tangent; its title and formal definition identify the inverse tangent used here.

Enter −1, −0.5, 0, 0.5 and 1 in A2:A6. In B2 enter:

=ATAN(A2)*180/PI()

Fill down. Expected results are −45, approximately −26.565051177, 0, approximately 26.565051177, and 45 degrees.

Negating a ratio negates its principal angle. The output is bounded even though the input ratio is not restricted to −1 through 1 as ASIN and ACOS are.

For a fictional rise of 3 over a positive horizontal run of 4:

=ATAN(3/4)*180/PI()

Expected angle: approximately 36.869897646 degrees. The ratio is opposite divided by adjacent for the chosen right-triangle orientation.

The run must be nonzero to form this quotient. With two signed coordinates, ATAN2 retains quadrant information that is lost by division into a single ratio.

Enter numeric 8 in C2 as a percent number, with a heading Percent grade:

=ATAN(C2/100)*180/PI()

Expected angle: approximately 4.573921260 degrees. A ratio of 0.08 corresponds to an eight-percent rise/run relationship.

If C2 instead contains a stored percentage value of 8%, its numeric value is already 0.08. In that separately defined setup use =ATAN(C2)*180/PI() without dividing by 100 again. An identical-looking heading does not tell you which representation was entered.

Coordinates (4,3) and (−4,−3) both give y/x=0.75. Applying ATAN to either quotient produces approximately 36.869897646 degrees.

Those two points lie in opposite directions from the origin. Their coordinate-based directions are approximately 36.869897646 and −143.130102354 degrees under ATAN2’s signed convention. A single ratio cannot retain both original signs.

This is why an unrestricted claim that ATAN(y/x) always equals ATAN2(x,y) is incorrect. The equality works without a quadrant correction for positive x; negative x requires the direction information preserved by the two-argument function.

=TAN(ATAN(2))

The mathematical expectation is 2. Starting with a finite ratio, ATAN returns its principal angle and TAN recovers the ratio.

By contrast, =ATAN(TAN(135*PI()/180))*180/PI() has expected principal result −45, not 135. Tangent repeats every 180 degrees, and ATAN selects the representative within its own principal interval.

=ATAN(100)*180/PI() is approximately 89.427061302 degrees, close to but below 90. It does not mean the input was 100 degrees. Display rounding to 90 can hide the distinction between a finite ratio and a vertical direction.

The official source establishes the inverse definition and radian convention, but does not specify every native extreme-input, coercion or error rule. Keep exact inputs and unrounded outputs when checking a sensitive calculation, and do not substitute another product’s error table for WPS evidence.

• WPS Academy: ATAN lesson, 2019-06-12 (Chinese; Windows Personal scope).
• Editorial testing standards.

The direct WPS product lesson supports the stated function scope. Worked outputs are independent expectations, not captured native results or proof of support across all current WPS clients.