A Knob for Scrolling Long Agent Output

The KM16 Macropad ($119) is sixteen keycaps on anodised aluminium, with one large knob and two small ones. The large knob is why people buy it for reading agent output. When an agent hands back a four hundred line diff, you have to travel through all of it, and a knob turns that travel into one continuous motion your hand never leaves.

What does turning the knob actually do?

A rotary encoder reports steps as you turn it, and each step fires whatever you mapped to it, exactly as though a key were being pressed very quickly. Map it to the up and down arrows and you move a line at a time. Map it to page up and page down and you move a screen at a time. Map it to your terminal's own scrollback binding and it moves the pager rather than the shell.

The knob holds no opinion about what it is scrolling, which is why it behaves identically in a Claude Code session in a terminal, a diff view in Cursor, and a pull request in a browser. Whether the knob also clicks inwards as a key depends on the unit, so confirm that before you plan a mapping around it.

Does a knob beat a scroll wheel or a trackpad?

For a long linear read, yes, and for one specific reason: the knob is a fixed point. Your hand arrives once and stays for the whole file, where a trackpad wants a repeated swipe and a mouse wants you to let go of the keyboard entirely. Knob scrolling is also steady rather than inertial. There is no flick and no overshoot, so you stop where you meant to instead of chasing a paragraph that slid past.

Against that, a trackpad is already under your hand and costs nothing. If you read diffs with two fingers and it has never once annoyed you, this is not a problem you have.

One big knob, or several small ones?

The KM16 gives you a large knob and two small ones, which suits a reviewer who wants scrolling on the big one and something coarser, such as moving file to file, on a small one. The Left-Hand Pad ($49) carries two rotary knobs above twelve keys in four columns of three, sold for macOS. The EM Mini Pad ($75) has a single knurled knob and five keys in a very small, very heavy aluminium block, wired over USB-C or connected over Bluetooth. The Voice Pad ($79) also carries one knob beside its microphone key, which is plenty if scrolling is the only turning you do.

What will a knob not fix?

Scrolling is the easy half of reading a long diff. The hard half is jumping: to the next hunk, to the one file you actually care about, back to the definition of the thing that changed. Those are searches and jumps. They are keys, not turns, and a knob makes none of them quicker. If your review pain is mostly navigation rather than travel, spend the keys on that and let the knob carry you through the stretches you genuinely read in order.

A knob also cannot read the diff for you. It moves the viewport, and every judgement about what deserves your attention stays yours.

For deciding what the keys around that knob should do, see our note on how to map a macropad for code review.