There are four reasons why your Philips health band is not measuring correctly. Luckily, each one is easily corrected. They are as follows:

Sensor placement
Philips health band should be tight but not uncomfortable on your wrist. The sensor should be in direct contact with your skin and your wrist should be clean and dry. Skin contact may be lost due to excessive hand or wrist movement. In that case, try repositioning the health band higher up on your wrist, or on the other hand.

Sending light through the skin
The health band should be able to transmit light through the skin. This way you will get the most correct measurement out of your health band. Tattoos on the wrist area might cause inaccurate measurements as less light is transmitted through the skin.

Sufficient blood flow
To get the right measurements with Philips health band there needs to be enough blood flowing through the skin. Try to  not wear the health band too tight as this may reduce the blood flow. Try loosening the strap a notch to relieve some pressure, but make sure the health band still keeps a tight fit.

Personal settings
The personal settings in the app are not correct, leading to inaccurate measurements. Always make sure that your personal settings in the app are correct.

For more information please see 'Syncing and storing personal health data' in the manual.