Typically, incorrect heart rate data originates in the Heart Rate Monitor (HRM) and not in the device.

If the device is reporting high heart rate spikes or an irregularly low heart rate there are a few things that may be at fault.

Tips to eliminate erratic heart rate data

• Apply moisture to sensors and contact patch using water;
• Make sure the module had been correctly positioned. the left side should be placed on the left side of your body.    
• Adjust the strap length to fit your chest to your arm.
• Warm up for 5–10 minutes before an activity.

• Avoid strong electromagnetic fields and 2.4 GHz wireless sensors, such as high voltage power lines, microwave ovens, 2.4 GHz cordless phones and other wireless access points.

Other possible causes of erratic heart rate data:

• Medicine, such as Beta blockers, and devices, such as pacemakers or implantable cardiac defibrillators could potentially interfere with HRM readings. Consult a physician regarding this possibility and for possible solutions.
• NOTE: For HRMs that have a removable module, ensure the module is cleaned and dried regularly after use to avoid the build up of rust and corrosion. 

Being aware of possible troubleshooting steps and causes for erratic HRM data will help ensure the best possible experience when using a HRM.