Write angle value in a modbus table

[shimano]

Hi!
I used the exemple code from Adafruit_LSM303_U librairie to create an inclinometer.
It works great but when I want to write the tilt (theta value) in my modbus table, it writes 45 or 225...
I really don't get it.
If you have any idea about what's going on, I would be happy to read you

Here's my code :

#include <Wire.h>
#include <Adafruit_Sensor.h>
#include <Adafruit_LSM303_U.h>
#include <math.h>
#include <ModbusRtu.h>

#define TXEN  4

/* Assign a unique ID to this sensor at the same time */
Adafruit_LSM303_Accel_Unified accel = Adafruit_LSM303_Accel_Unified(54321);

/* Here are the variables used */
float theta; //angle theta pour l'inclinaison 
float acc_x;
float acc_y;
float acc_z;
float g = 9.81;

Modbus slave(1,Serial,TXEN);      //Slave Nano                      // this is slave @1 and RS-485
  int au16data[17] = { 0, 0, 0, 0, 0, 0, 9999, 9999, 0, 0, 9999, 0, 0, 0, 9999, 9999, 9999 };  //Les trois derniers chiffres du tableau sont accéléromètres X Y Z
 
void setup()
{
  while (!Serial);
  Serial.begin(19200);
  slave.start();
  
}

void loop()
{
  get_Inclinaison();
  slave.poll( au16data, 17 );
}

void get_Inclinaison(){
/* Get a new sensor event */
  sensors_event_t event2;
  accel.getEvent(&event2);

  acc_x = event2.acceleration.x;
  acc_y = event2.acceleration.y;
  acc_z = event2.acceleration.z;
  theta = atan2(acc_x/9.81,acc_z/9.81)/2/3.141592654*360; /*Should be in degrees*/
  
  if (theta < 0)
    {
      theta = theta + 360;
      au16data[9] = (int)theta;
     
    }
    else 
    {
      au16data[9] = (int)theta;
      }
   
  }

Thanks in advance.