epa04698251 A collection of Apple's new watch lie on a table during a preview day at the Apple Store in Covent Garden in London, Britain, 10 April 2015. Apple's latest offering went on display on 10 April in stores. Apple started to take pre-orders online for the Apple Watch which will go on sale from 24 April 2015. EPA/ANDREW COWIE

It's official: the Apple Watch just doesn't play well with tattoos.

After a number of Apple Watch buyers with tattooed wrists reported that their ink appeared to be interfering with the Watch's ability to read their heart rates. On Friday, 9 to 5 Mac spotted an update to the company's support page for the watch that confirms the problem.

[The Apple Watch, like your grandmother, has a problem with your tattoos.]

The document seems to back user reports that darker, more solid tattoos cause the most interference, and also confirms that the problems occur because the light-based technology Apple uses to measure your heart rate. Apple measures blood flow in part by shining green light -- which your red blood absorbs -- into your wrist. It then calculates your pulse by tracking how much of that light gets absorbed.  But, it seems, the light can have problems getting through tattoo ink to get an accurate reading.

"The ink, pattern and saturation of some tattoos can block light from the sensor, making it difficult to get reliable readings," the document says. There is no indication from Apple that variations in natural skin tone cause similar problems; the ink seems to be main problem here.

Being able to measure fitness statistics is one of the main selling points for the Apple Watch, and is the focus of one of its latest ads for the device. The success of companies such as Jawbone and Fitbit have shown that there is a wearables market out there for fitness buffs, and it's probably one of the easiest markets for Apple to tap into in the early days of its Watch launch.

However, Apple does caution instances in which the Apple Watch may have trouble reading your heart rate.

The obvious example is when the watch is too loose and its sensors aren't in contact with your skin. But Apple said the device can also have problems when it's being jostled at irregular intervals --  such as when you're playing tennis or boxing --  or when it's cold outside and your blood may be shunted away from the surface of your skin as part of your body's natural response to lower temperatures.

If any of those are a persistent problem for you, the company said, you may want to invest in a separate chest-strap monitor -- one, of course, that can be paired with the Apple Watch.