int servoPin = A4;
Servo akshayServo;
int servoPos = 0;
int lastPrice = -1;
int percChange;

void setup() {
    
akshayServo.attach(A4);

Particle.function("servo", servoControl);

Particle.variable("servoPos", &servoPos, INT);
}

void loop() {

}

int servoControl(String command){
  // Convert
   int newPrice = command.toInt();
   // Make sure it is in the right range
   // And set the position

if(lastPrice == -1){
        servoPos = 90;
    }

else{
    
    percChange = (newPrice - lastPrice) / lastPrice;
    
    servoPos = constrain((percChange*10) + 90, 0 , 180);
}
   // Set the servo
   akshayServo.write(servoPos);
   
   lastPrice = newPrice;

   // done
   return 1;
}