What it is

The calculator your paper tablet is missing. A Quick Settings tile opens a floating scientific calculator over whatever you're working on — a notebook page, a PDF, a textbook. Work the problem by hand, tap the tile, compute, tap × and keep writing. The screenshot is exactly that: a Bayes' theorem exercise worked in ink, with 0.86 × 0.05 ÷ 0.24 evaluated in place.

Features

One tap from anywhere — QS tile opens/closes the overlay on any screen, documents included.
Proper scientific set — trig + inverses (SHIFT), log/ln/10ˣ/eˣ, powers and roots (x², x³, x^, √, ³√, x⁻¹), Abs, factorials, nPr/nCr, %, π/e.
Casio habits respected — two-line display (expression above, result below), implicit multiply, trailing close-parens optional, Ans, independent memory (M+/M−/MR), DEG/RAD, and S⇔D decimal↔fraction.
Self-contained + private — a pure QML/JS evaluator (no eval()), no network, no telemetry, nothing leaves the device. The shipped patch is plaintext — you can read every line before installing.
Co-tenant safe — every QML id is namespaced so it won't collide with other installed qmd tweaks.

Requirements

reMarkable Paper Pro, firmware 3.26.0.68.
xovi + the qt-resource-rebuilder extension (free; links in the README).
No other paid item required.

Install

Copy one file to the device, restart xochitl the xovi-safe way (exact commands in the README), and the tile appears in Quick Settings. Uninstall = delete the file, restart. No system files are modified on disk.

How it changes your device

This product modifies the on-device user interface at runtime. It contains no reMarkable software; changes are applied to files already present on your device and are fully removed by uninstalling.

Honest caveats

This one patches the system UI via qmldiff (that's what makes a QS tile possible) — unlike our AppLoad apps. The README includes the one-line SSH recovery should any qmd on your device ever misbehave: delete the file, restart. Nothing persistent is touched.
qmldiff patches are firmware-sensitive; tested on 3.26.0.68, updates best-effort after firmware releases.

Calculator — Quick Settings scientific calculator