The Steel HR collects data on heart rate using photoplethysmography (PPG) and calculates a measurement based on dedicated algorithms. PPG uses light absorbed by the blood and skin to measure the variation in blood flow to the veins, which can be used to calculate the heart rate. That is why it may be difficult to obtain an accurate measurement if the Steel HR is not worn optimally.

To obtain the most accurate results please follow these guidelines:

• The Steel HR should be worn tightly enough that the sensor on the back of the watch face touches your skin.
• Wear the Steel HR 1 to 2 finger width away from your wrist bone.
• Use the wristband Withings provides with your Steel HR.
• Make sure that your watch stays in place during exercise. If it moves around at all, tighten your band one notch.
• Make sure your band is secure, but not too tight. It should be comfortable and allow proper circulation.
• Make sure the watch is clean, so the green LEDs are not obstructed by dust or dirt.

Additional factors that can cause the heart rate to be measured inaccurately:

Skin perfusion

Skin perfusion, or how much blood is flowing through the skin, varies among individuals and according to the environment. In certain circumstances, the Steel HR may not be able to provide an accurate heart rate measurement.

Skin and blood properties

The technology used by the Steel HR is based on the light absorbed by your skin and blood. Any permanent or temporary changes to your skin, such as tattoos, sweat, or even hair on the wrist may affect the measurements.

Environment

Environmental factors may affect the ability of the Steel HR to take an accurate measurement. For example, water may obstruct or modify the light dispersion, and cold weather may impact skin perfusion.

Motion

The Steel HR needs to stay securely in place to provide a heart rate measurement. Activities that cause force to the wrist, such as boxing or volleyball, may not allow the Steel HR to provide an accurate heart rate measurement.