  // WARNING: Necessary for all users, Here are all the resistance values ​​you need to apply for supported sensors:

 /* MQ135:     20  kΩ
  * MQ2:       5   kΩ
  * MQ3:       200 kΩ
  * MQ4:       20  kΩ
  * MQ5:       20  kΩ
  * MQ6:       20  kΩ
  * MQ7:       10  kΩ
  * MQ8:       10  kΩ
  * MQ9:       10  kΩ
  * MQ131_LOW: 20  kΩ
  * MQ131:     20  kΩ
  * MQ136:     20  kΩ
  * MQ137:     47  kΩ
  * MQ138:     20  kΩ
  * MQ214:     50  Ω --> 0.05kΩ
  * MQ216:     50  Ω --> 0.05kΩ
  * MQ303A:    47  kΩ
  * MQ303B:    10  kΩ
  * MQ306A:    10  kΩ
  * MQ307A:    1   kΩ
  * MQ309A:    10  kΩ
  */

  /* The graph shows the recommended resistance values specified in each sensor's datasheet as the most accurate operating points.
  *  Although the datasheets also indicate broader operational ranges beyond these ideal values,
  *  the library enforces the use of only the optimal ones to ensure consistent measurement accuracy. */
