ATAN
ATAN(number) returns radians from -pi/2 to pi/2; ATAN2 covers the full circle. Worked examples and the degree conversion. Matches Excel.
Syntax
ATAN(number)| Argument | Required | Description |
|---|---|---|
number | Required | A tangent value — any number. |
Examples
Every example below was executed against VisiGrid engine 0.54.0 — not
transcribed from another vendor's documentation. Reproduce any of them with vgrid calc.
| Formula | Result | Notes |
|---|---|---|
=ATAN(1) | 0.79 | π/4 radians. |
=DEGREES(ATAN(1)) | 45 | A slope of 1 is 45 degrees. |
=DEGREES(ATAN(-1/-1)) | 45 | A point down and to the left gives the same slope, so ATAN cannot tell it from up and to the right. |
From a gradient to an angle
A road that climbs 8 metres every 100 has a gradient of 0.08. Its angle:
=DEGREES(ATAN(0.08))Any number is a valid input, so unlike ASIN and
ACOS, ATAN never returns #NUM!.
When to use ATAN2 instead
ATAN takes one number, a ratio, and a ratio has already lost the signs of the
two values that made it. -1 divided by -1 is 1, the same as 1 divided by 1, so
the angle comes back as 45 degrees when the point is really at -135.
ATAN2 takes the two coordinates separately and returns the
right quadrant. It also copes with a run of zero, which as a ratio would be a
division by zero.
Excel compatibility
Matches Excel. Returns radians between -π/2 and π/2.