Microsoft has inadvertently confirmed that it had a smaller Surface tablet ready to release when it unveiled the larger Surface Pro 3 last month.

Eagle-eyed observers today pointed out that the Surface Mini, a long-rumored small tablet, was referenced several times in the Surface Pro 3 User Guide, which is available online.

Microsoft started selling some models of the Surface Pro 3 in retail today, and began delivering devices that customers had pre-ordered since the May 20 introduction.

The Surface Mini was featured most predominantly in the user guide's discussion of the Surface Pen, a writing and sketching tool that comes with the Surface Pro 3, and apparently would have accompanied the smaller tablet, too. Mentions of OneNote, Microsoft's note-taking app, were scattered throughout the guide, including the sections where the Surface Mini was mentioned.

"Click the top button [of the Surface Pen] to open OneNote, even if your Surface is locked," the guide stated. "Bluetooth technology links your Surface Pen to your Surface Mini or Surface Pro 3, so when you click the button, your Surface responds instantly [emphasis added]."

That matches what some reported prior to Microsoft's May 20 event: The Surface Mini, those reports claimed, would be pitched as a note-taking device, and released in time for the back-to-school sales season.