The Design
Organic light-emitting diodes (OLEDs) utilising 262,000 colours are used in the Black BT screen to give a sharp, bright and customisable colour display. Even with my failing eyesight it was incredibly easy to see and read.
The 45mm screen sits behind a hardened polycarbonate window.
The body is CNC machined from a single block of high-grade polyacetal (Delrin), with just two large push-buttons to select and navigate menus. Two wrist-mounting options are supplied, with an elasticated, buckled strap or bungee chord threaded through four holes, one at each corner.
Power is provided by a Samsung li-ion 1190mAh battery. This is rechargeable via a USB port, providing several options for a charging source, such as laptops, phone or car chargers.
The USB charging cable also acts as a data transfer port, and information can be exported to any PC or Mac computer. The Black BT is instantly recognised as a mass storage device and files can be copied easily.
There is also the facility to upgrade firmware via the XDeep website.
The two balanced metal buttons have electronic press detection so they don’t need seals, and this helps the unit attain its 200m depth-rating.
The bottom-timer has three main displays available under water. The main screen provides current, average and maximum depth, total dive time and an ascent speed indicator.
The second screen shows a graph of your dive profile, and the third displays an advanced three-axis digital compass.
At the surface, a logbook function displays a very detailed record of your dives, and includes depth and temperature graphs.

Under Water
I took the bottom-timer with me for a week’s Caribbean shark-diving. On the first dive I opted for the elasticated strap and buckle set-up, and quickly found that it wasn’t up to the job.
It was tricky to adjust and felt flimsy and insecure on my arm – I worried throughout the whole dive about losing the instrument.
I switched to the bungee strap immediately afterwards, and never looked back. If the timer were mine I would have thrown the strap overboard at the first opportunity.
With the bungee fitted the unit sat securely on my arm, settling nicely between my wrist and forearm. The buttons were readily accessed and the display was easy to read at varying angles to my eyeline.
The colours on the bright OLED display can be customised, with a choice of pre-set themes from which to choose, or you can allocate a specific colour for whichever reading you like.
I opted for the standard scheme but had Baltic Green, Deep Blue, Pink Panther or Desert Storm themes available.
The buttons employ a short-push, long-push system to activate functions, scroll through menus or change screens. They’re very similar to those on the original VR3 computers which drove some tech divers (and tall, slim dive-gear testers) to distraction.
I, however, own and dive with a VR3 and so found the two-button system easy to use.
The instrument sparked into life automatically at around 1m in depth. The display was easy to read in the bright sun near the surface and just got better the deeper (and darker) I went.
The display is laid out in a logical manner, with a quick look providing all the critical information needed for the dive.
Battery-charge status is displayed in the top left corner and given as a percentage as well as a diminishing rectangle.
I discharged the battery after around 20 dives, the shortest of which was 70 minutes, culminating in a total dive-time of around 25 hours.
The display subsequently showed a message that read: “Battery too low. Sorry.”
Sorry Are you serious, an apologetic dive instrument That’s a first.
The recharge time depends on the voltage used. It took a little over five hours to fully recharge from my iPhone USB plug connected to a 110V outlet, and I suspect that it would have taken longer via my laptop, but I didn’t get the chance to prove it.
There are several alarm settings that can be pre-programmed, including depth, time, ascent rate and battery levels. There is also an alarm-clock function to ensure that you don’t oversleep and miss your full English breakfast.
The compass screen was very easy to access with a short left or right button push. The display still showed critical information in the form of current depth, time and ascent rate, but the bulk of the screen was filled with the compass graphics.
The direction of travel is shown in degrees along with a highly visible lubber line. The compass can also be programmed to allow a pre-determined route to be followed, and
a return course is automatically generated. It’s clever stuff.
After a day’s diving I accessed the logbook feature while plugged into my MacBook. It was easy to drag and drop data between folders and files and review profiles.

Those Polish designers have done an excellent job in developing and building this dive instrument. It’s ultra-bright, compact and works like a charm, and once you’ve got your head around the two-button menu and function system it’s very easy to use.
The elasticated strap was disappointing but the bungee made for a comfortable, secure and practical solution.
The compass is excellent, and I would purchase the Black BT for this function alone.
With most modern dive computers already having a Freedive mode, the question has to be asked: “Do you really need to buy a separate, dedicated bottom-timer
Well this is a bottom-timer and then some. If proof of the pudding is in the eating, the fact that demand for these little black boxes is outstripping supply tells me that tec-divers think the Black BT is a tasty pudding indeed.
The XDeep guys are going a step further, with firmware to convert this product into a full nitrox computer (Black EANx) or full mixed-gas trimix version (Black TMX) in the pipeline as downloadable upgrades. These upgrades may even be available as you read this review.
The Black BT looks a million dollars, but at under £220 it’s unlikely to break the bank, and is an excellent addition to any diver’s armoury.

SCREEN SIZE 45mm x 35mm
POWER Samsung 1190mAh li-ion
CHARGING USB via adaptor
DIVER GUIDE width=100% width=100% width=100% width=100% width=100% width=100% width=100% width=100% width=100% width=100%