Question about radians after a trigonometry formula

This is just a test from other full code that I’v made and my radians after I calculate it turns into a negative number. I’m probably doing it wrong but I think you guys can direct me about this and help me with it, I have no idea why it’s like that. Also don’t mind other variables that are not mentioned in the loop. Also the laserServo_Pos needs to be between 0° and 55°. And the distanceL should be maximum 40 cm

#include <Servo.h>

#define shaftServo_Pin 3
#define laserServo_Pin 9

const int echoPinL = 5;
const int trigPinL = 6;
const int echoPinR = 10;
const int trigPinR = 11;

int laserPin = 2;

int shaftServo_Pos;
int laserServo_Pos;

Servo shaftServo;
Servo laserServo;

int distanceL;
int distanceR;

  int leftside;//if the object is on the left side 1=true, 0=false
  int rightside;//if the object is on the right side 1=true, 0=false
void setup(){
  int shaftServo_Pos = 90;
  int laserServo_Pos = 0;

  pinMode(echoPinL, INPUT);
  pinMode(trigPinL, OUTPUT);
  pinMode(echoPinR, INPUT);
  pinMode(trigPinR, OUTPUT);
  pinMode(laserPin, OUTPUT);

void loop(){
  float rad;

  long durationL;  
  digitalWrite(trigPinL, LOW);
  digitalWrite(trigPinL, HIGH);
  digitalWrite(trigPinL, LOW);
  durationL = pulseIn(echoPinL,HIGH);
  distanceL = (durationL/ 2 ) * 0.0343;
  Serial.print("Distance: ");
  rad = tan(distanceL + 2.26 / 15.35);//"2.26" distance from the front edge of the sensor to the shaft, "15.35" length from the middle of the sensor to the top hinge
  Serial.print("Radian: ");
  laserServo_Pos = ((rad * 4068) / 71)-15;
  if(laserServo_Pos <= 55 && laserServo_Pos >= 0){//not permanent just temporarily
  Serial.print("Laser servo pos: ");


Here is my “test bench”.

are you sure of your maths? the tangent function takes an angle (in radian) and returns its tangent, so something between negative infinity and infinity… it’s not an angle. Why do you call that rad? are you expecting an angle?

tan(x) = distance between I and P

Use either atan() or atan2() to get an angle from two distances.

Yeah I’m expecting an angle. I knew that I was wrong somewhere. I need to calculate an angle to tell a servo in what position it should be. Also I’m still new to the arduino platform and coding. And thank you for your response.

Thank you, I’ll try that.

Not to be pedantic or anything, but…

…it true only if the distance between O and I is one.
Generally, tan(x) = IP / OI

correct, that was supposed to represent the Unit circle but I did not mention it

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