The new iPad Pro has it all thanks to the M1 chip and other hardware upgrades. There is no doubt that Apple has given the iPad Pro a worthy upgrade. But be careful: A small detail makes a big difference.

As part of the first Apple event this year, Apple presented a lot of new products, such as a new iPhone 12 and 12 mini in purple, lots of new (and above all colourful) iMacs in a new design and with an M1 chip and also the long-awaited AirTags  (Apple’s Bluetooth trackers that make ‘stupid’ objects smart) have finally seen the light of day. Not to forget the new iPad Pro models.

Apple is equipping the 2021 iPad Pro with loads of new features that make the iPad Pro – once again – the best tablet of all time. Outwardly, the 2021 iPad Pro looks a lot like its predecessor, but a closer look at the spec list shows that even the smallest differences can have a big impact in the end.

It’s 0.5mm thicker.

This is an important difference between the generations that will not be immediately obvious to potential buyers. While the 12.9in model from 2020 has a depth of 5.9mm, the dimensions for the new M1 iPad Pro 6.4mm. This means that the new device is 0.5mm thicker – and that means that cases designed for last year’s 12.9in iPad Pro and Apple’s own Magic Keyboard for 12.9in iPad Pro that it introduced last year will not be compatible with the new device. This is why Apple is now selling a new Magic Keyboard specifically for the iPad Pro 12.9‑inch (5th generation), although it is backwards compatible with other 12.9in iPads.

Complicating matters, because both 12.9-inch models have the same height and width, the new iPad Pro should actually fit into a 2020 Magic Keyboard. However when users want to close the iPad Pro from 2021 while it is attached to the Magic Keyboard it will not close.

If you take a look at the product description of the Magic Keyboard, you will see that the iPad Pro 2021 is not compatible with the older Magic Keyboard. However, this only applies to the 12.9-inch iPad Pro. The 11-inch iPad Pro from 2020 and 2021 are both compatible with the old Magic Keyboard.

This will only be a problem for those users who already own the older Magic Keyboard for the 12.9in iPad and want to upgrade to a new 12.9-inch iPad Pro. If they wish to continue using a smart keyboard from Apple they also need to buy the new Magic Keyboard – it costs £349/$349 – buy one here UK and here US. While this model will work with older 12.9in iPad Pro the old keyboard that Apple used to sell will not work with the new model.

Otherwise, the 12.9in iPad Pro 2021 and iPad Pro 2020 can look like twins at first glance. Both models are 280.6mm high and 214.9mm wide. The weight differs slightly, but the difference is so small that it shouldn’t be particularly noticeable in everyday life.

This article originally appeared on Macwelt. Translation by Karen Haslam.