You literally can't wear your heart on your sleeve

In one of this week's more interesting discoveries, Apple Watch sensors appear to be negatively affected by the presence of heavy arm tattooing, also known as sleeves.

One of the functions offered by the device is heart rate measurement at 10-minute intervals throughout the day. The results are recorded and stored in the Health app and used in combination with other information to estimate calories burned and heart rate reaction to specific workout intensity levels.

According to information published on the Apple website: "The heart rate sensor in Apple Watch uses what is known as photoplethysmography. This technology, while difficult to pronounce, is based on a very simple fact: Blood is red because it reflects red light and absorbs green light. Apple Watch uses green LED lights paired with light-sensitive photodiodes to detect the amount of blood flowing through your wrist at any given moment. When your heart beats, the blood flow in your wrist - and the green light absorption - is greater. Between beats, it’s less. By flashing its LED lights hundreds of times per second, Apple Watch can calculate the number of times the heart beats each minute - your heart rate."

All well and good, but it turns out that the ink pigmentation present in heavily tattooed skin interferes with the sensor, as the light's reflectiveness is reduced. Many wearers of the new technology have discovered that certain ink colours affect operation more than others (darker colours impact more), resulting in everything from heartbeat misreads through to device lock-ups requiring password entry.

It doesn't seem like there's any way around it and the Apple website was updated 29 April to reflect this issue.