Dotori Roman Numerals

Dotori Roman Numerals converts between ordinary numbers and Roman numerals, in both directions, as you type. Tap either box to choose which side you are editing; the other side updates with every key.

There is no system keyboard. Each box has its own keypad — digits for the Arabic side, the seven Roman letters for the other — so the controls never jump and half the screen is never covered.

Key features:

- Both directions, live. Type 1990 and MCMXC appears; type MCMXC and 1990 appears

- A keypad built for each side. Roman keys are laid out in value order: I V X / L C D / M

- Numbers past 3999, written the classical way. A bar over a group multiplies it by 1000 and a second bar multiplies it again, so 4000 is IV with one bar and 4,000,000 is IV with two. The app draws every bar itself rather than relying on a font, and covers 1 to 3,999,999,999

- Non-standard forms are read, not rejected. IIII, VV and IC all give a value, and the app shows you the standard spelling next to it

- A breakdown you can open: 1990 = M (1000) + CM (900) + XC (90)

- A help page covering the seven symbols, the six subtractive pairs, the repetition limits, the overline rule, and exactly how this app reads non-standard input. Every example is tappable — press one and it loads into the converter

- Dark and light themes, English and Korean, and a screen-orientation choice

- Works entirely offline. No account, no network access beyond the ad banner

Known limits:

- The app starts at 1. Roman numerals have no symbol for zero and no way to write a negative number or a fraction

- There is no text selection or clipboard support yet; tap a digit or letter to put the cursor there and edit from that point

- The overline is drawn, so a screen reader cannot see it as a line. The value box states it in words instead — "overlined I V times one thousand, then X I I, value 4012"