Dotori Roman Numerals — user manual

com.droidactor.roman

Converting

The screen has two boxes — Arabic on top, Roman below — and one keypad underneath. Tap a box to edit that side; the keypad changes to match, and the other box follows every key you press.

Type 1990 on the Arabic side and MCMXC appears below.
Type MCMXC on the Roman side and 1990 appears above.
Tapping a box never changes its contents. The side you last edited is the one the other is derived from, so you can look at what you typed without it being rewritten.
Tap a digit or letter to put the cursor there and edit from that point. AC clears both boxes; the backspace key removes the character before the cursor.

Values past 3999 — the overline

A bar over a group of letters multiplies that group by 1000, and a second bar multiplies it again. IV with one bar is 4000; IV with two bars is 4,000,000. Two bars are a later convention rather than ancient Roman practice, and no font carries them, so the app draws every bar itself. It covers 1 to 3,999,999,999.

The Roman keypad has two buttons at the top — Plain and ×1K and ×1M. They choose which part your next letters go into:

Press ×1K and type IV — the value is 4000.
Press ×1M and type IV — the value is 4,000,000.
Press Plain and type XII — the value becomes 4012.

Each part keeps its own cursor, so you can go back to the overlined part and correct it without losing your place in the other.

What the app accepts

Forms like IIII, VV or IC are not standard, but the app still reads them — clock faces really do use IIII. Each symbol is subtracted when the next one is larger and added otherwise, so IIV reads as 5 (1 − 1 + 5). Other tools may read it differently.

Whenever your input is not the standard spelling, the status line shows the standard one next to it. That is a note, not an error — the value is still converted.

The breakdown

Under the boxes is Show how it breaks down. Open it and the current value is split into the parts that make it: 1990 becomes M (1000) + CM (900) + XC (90). It follows what you type, and stays open until you close it.

The help page

The ? button in the header opens a page covering the seven symbols, the six subtractive pairs, how often a symbol may repeat, the overline rule, and how this app reads non-standard input. Every example there is tappable — press one and it loads into the converter so you can see it convert.

Settings

Theme: dark or light. This is an app setting, not the phone's.
Language: follow the system, or choose Korean or English.
Screen orientation: follow the system, auto-rotate in this app, or lock to portrait or landscape. In landscape the boxes and the keypad sit side by side.
Privacy options: reopen your ad consent choices.

Troubleshooting

Symptom	What to check
A key does nothing	The Arabic side takes at most 7 digits and each Roman part at most 20 letters. At the limit further letters are refused — the key still responds, but the value does not change.
“This app covers 1 to 3,999,999,999”	The value is outside the range. Roman numerals have no zero and no negatives, and the overlined part on its own cannot exceed MMMCMXCIX (3999).
“That is not a Roman numeral”	The Roman box contains something outside I V X L C D M.
Letters go into the wrong part	Check which of Plain / ×1K / ×1M is selected — it decides where the next letter lands.
The cursor is not where you expect	Tap the digit or letter you want to edit next to it. Editing one box moves the other box's cursor to the end of its new value.

Requirements, limits, and privacy

Android 8.0 or newer
Works offline — conversion never uses the network
No account, no sign-in

Nothing you type is stored or sent anywhere; it is gone when the app closes. The app keeps only the theme, display language and screen orientation you chose. See the full privacy policy.

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