A diagnostic instrument with NDIR non-dispersive infrared sensor to carry out accurate CO2 measurements and the evaluation of air quality systems in schools, offices, hospitals, companies, etc. Range: 0 to 5000 ppm; resolution 1 ppm; accuracy: ±3% of reading ±50 ppm at 25ºC; response time: 20 sec; max, min and average value function; working conditions: 5-45ºC, 80% RH without condensation; dimensions: 244 x 84 x 44 mm; weight: 270 g; power: 4 AA alkaline batteries or AC adapter.