Sizing & Fit
In this article
Start here
Fit affects accuracy more than anything else. The sensor reads light through your skin, so if there's a gap between the device and your wrist, readings go patchy. Snug but not tight, sitting flat, about a finger's width above the wrist bone.
The Pro is one size and adjusts to fit, so there's nothing to measure before you order.
Where to wear it
On the top of your wrist, a finger's width above the wrist bone, with the sensor sitting flat against the skin. Not on the bone itself, and not down on the hand side of it - both leave gaps.
Either wrist works. Most people wear it on the non-dominant one because it gets knocked about less and moves less during the day, which gives steadier readings.
How tight it should be
Tight enough that it doesn't slide when you turn your wrist over, loose enough that you can just get a fingertip underneath.
- Too loose shows up as gaps in your heart rate, missing sleep, and step counts that look low.
- Too tight leaves a mark, gets uncomfortable after an hour, and doesn't make readings any better.
If you've had it on for a while and there's a deep line in your skin when you take it off, go a notch looser.
Putting it on
The Pro comes on a woven strap that fastens with hook and loop. There's no buckle.
- Feed the tail through the metal loop and pull it all the way back through.
- Pull it back on itself until the strap is snug, with the module on top a finger's width above the wrist bone.
- Press the tail down flat onto the strap so the hook and loop grips.
Press it down along as much of its length as you can rather than just the end, since a tail fastened only at the tip is the one that lifts and catches on a sleeve.
Your strap and sport
The woven strap is treated to resist bacteria, so it doesn't build up odour the way an untreated fabric strap does. You can train and swim in it without swapping to anything else - just rinse it in clean water after a heavy session and let it air dry.
Changing the strap
The strap is held on by spring bars, the same as a watch, with one at each end of the module.
- Lay the device face down on a soft surface so you don't scratch it.
- Press the end of the spring bar inwards to compress it, and lift that side of the strap free. A spring bar tool makes this easy, and a small flat screwdriver or a fingernail will usually do it.
- Line the new strap up, hook one end of the spring bar into its hole, compress the other end and let it click into place.
- Give the strap a firm tug before wearing it, to check both bars have seated properly.
Take your time on the second bar - that's where most people slip and mark the case.
Wearing it for exercise
Move it an inch or two further up your arm and tighten it by one notch before you train. Wrist movement during weights, boxing and anything with a grip is the main cause of dropped heart rate readings. Loosen it again afterwards.
Wearing it in bed
Keep it at the same tightness you wear it during the day. People often loosen it for comfort at night and then wonder why their sleep data has gaps in it. If it's uncomfortable to sleep in at daytime tightness, it's probably too tight in the daytime too.
If it marks or irritates your skin
Almost always moisture and friction rather than the materials themselves.
- Loosen it slightly and move it a centimetre or two up or down your wrist.
- Take it off after workouts and let both your skin and the strap dry properly.
- Rinse the strap in clean water if you've been sweating in it, and let it dry fully before putting it back on.
- Give your wrist a break for an hour or two a day.
If irritation carries on after all that, stop wearing it and speak to a pharmacist or your GP. Get in touch with us too and we'll sort a different strap out.
It won't fit
The strap covers most wrists, but if it's at the end of its adjustment either way, message us with your order number and your wrist measurement and we'll sort one that fits.
Was this article helpful?