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Aleksei Novichkov edited this page Jun 26, 2026 · 1 revision

Compio is a notebook-style editor for everyday math. Each line is either a calculation or a variable assignment; results appear at the end of the line as you type.

How documents work

  • One expression per line. Each line is evaluated independently.
  • Results on the right. A line like 2 + 2 shows = 4 at the end.
  • Variables. Use name = expression (or name: expression) to store a result and reuse it on later lines.
  • Order matters. Variables are available only on lines below the line where they are defined.
monthly = 4200 EUR
rent = 1450 EUR
left = monthly - rent

Lines without = or : are plain expressions — they calculate but do not create a variable:

2 + 2          → 4
10 km in mi    → 6.21 mi

Quick reference

Copy the block below into the editor as-is:

// Variable — result is stored under the name
width = 12

// One-off calculation — no variable
2 + 2 = 4

// Comment lines and headings are ignored by the calculator
# Example header

// Precedence: ^ before * / %, then + -
2 + 2 * 3 = 8
2 * 2 ^ 3 = 16
2 ^ 3 ^ 2 = 512

// Grouping — parentheses override precedence
(2 + 2) * 3 = 12
(3 + 2) * 10 = 50

// Unary minus binds after exponentiation
- 4 ^ 2 = -16
(- 4) ^ 2 = 16

// Scientific notation
6.02214076e23 = 6.02214076e+23
1.5e3 km // 1500 km = 1 500 km

// Functions (see Functions menu for the full list)
sqrt(16) = 4
round(3.7) = 4
num(12 EUR) = 12

// Aggregation — sum lines above within a group
rent = 100
food = 50
sum() = 150

// Units — attach to numbers, mix compatible ones, convert with in / to / as
100 USD = 100 USD
10 cm + 1 m = 1.1 m
//will convert to euros
10 USD in EUR
100 cm in m in km = 0.001 km

Numbers

Integers and decimals

42
0.123
-2

Thousands separators

Use spaces or commas in the integer part to make large numbers readable:

1,233,232
1 999 232
1,233,232.232

Commas are allowed only in the integer part (before the decimal point).

Underscores work the same way:

1_233_232
34_500_000

Scientific notation

Write very large or very small numbers with e or E:

6.02214076e23
1.23e-7
2e10
1E+10

You can attach units to the mantissa:

1.5e3 km    → 1500 km

Results may also display in scientific notation when a plain decimal string would be unwieldy.

Negative numbers

Unary minus works on numbers and expressions:

-2
-40 / 2
2 + -3
(-4)^2

Variables

Assign a name with = or ::

tax_rate = 0.21
net: 100
gross = net + net * tax_rate

Naming rules: names start with a letter (including non-Latin letters) and may contain letters, digits, underscores, dots, and spaces. Spaces join words into a single name — monthly net is one variable, not two:

pi_approx = 3.141592653589793
debt_per_capita = total / population
monthly net = 4_200 EUR
π = 3.141592653589793

Use variables in later expressions:

x = 9
sqrt(x)
2 + x

Variables can carry units:

width = 12 EUR
trip = width * 14

Operators

Arithmetic

Operator Meaning Example Result
+ Addition 2 + 3 5
- Subtraction 10 - 4 6
* Multiplication 3 * 7 21
/ Division 12 / 3 4
% Remainder (modulo) 10 % 3 1
^ Exponentiation 2^4 16

Parentheses override precedence:

(2 + 2) * 3    → 12
2 + 2 * 3      → 8

Operator precedence

From highest to lowest precedence:

  1. Parentheses ( … )
  2. Exponentiation ^ (right-associative: 2^3^2 = 2^(3^2) = 512)
  3. Multiplication, division, remainder *, /, %
  4. Addition and subtraction +, -

Unary minus has lower precedence than exponentiation:

-4^2     → -16    (negates 4²)
(-4)^2   → 16     (squares -4)

Powers and roots

Fractional exponents follow real-number rules. Some combinations yield NaN (not a real result):

16^0.5       → 4
16^(1/2)     → 4
(-4)^0.5     → NaN
(-8)^(1/3)   → NaN

For n-th roots — especially odd roots of negative numbers — prefer the root function (see Functions).

Functions

Functions are called by name with parentheses. Arguments are separated by commas. Open the Functions menu in the editor toolbar to browse every built-in function with short descriptions.

Everyday functions

These cover most day-to-day math:

Function What it does
sqrt(x) Square root
abs(x) Distance from zero, or simpler — drop a sign
floor(x), ceil(x), round(x), trunc(x) Round down, up, to nearest, or drop decimals
num(x) Drop the unit from a value (keep the number)
pow(base, exponent) Raise to a power (pow(2, 8) = 256) 
sqrt(16)              → 4
abs(-7)               → 7
round(3.7)            → 4
num(12 EUR)           → 12
pow(2, 10)            → 1024

root(x, n)

The n-th root of x. The degree n is the second argument. Unlike ^, root handles odd integer roots of negative bases correctly.

root(16, 2)     → 4      (square root)
root(27, 3)     → 3      (cube root)
root(-8, 3)     → -2     (odd root of negative base)
root(-4, 2)     → NaN    (even root of negative base)

For other roots and powers, see More roots and Exponents & logs in the Functions menu (cbrt, exp, ln, log, and more).

More functions

The Functions menu groups the rest by topic: Totals, Compare & limit, Trigonometry, Exponents & logs, and Advanced. Use autocomplete while typing a function name to see argument hints.

Functions preserve units from their input when the operation allows it:

x = 9 mm
sqrt(x)    → 3 mm

Aggregation functions

sum(), average() (alias avg()), and median() summarize the preceding lines in the current group. They take no arguments. Blank lines separate groups — aggregation stops at the group boundary.

rent = 1_450 EUR
utilities = 185 EUR
groceries = 520 EUR
sum()   → 2155 EUR

10
20
sum()   → 30

10

20
sum()   → 20   (only lines after the blank line)

Aliases: total() is the same as sum().

Use aggregation inside larger expressions:

10
20
2 + sum()   → 32

All aggregated lines must use compatible units (or plain numbers). sum() on the first line of a group returns 0; average() and median() need at least one preceding line.

Units and conversions

Writing values with units

Attach a unit directly to a number, or separate them with a space:

100USD
100 usd
12 EUR
3.5 km
250 g

Unit names are case-insensitive for matching (usd, USD, Usd all work). The canonical spelling is kept in results when possible.

Supported units

Currencies — ISO 4217 codes (e.g. USD, EUR, GBP, JPY, RUB). Exchange rates are fetched live from the Frankfurter API when you convert between currencies.

Measurement units — length, mass, volume, time, area, temperature, and more. Examples:

Category Examples
Length m, cm, km, mi, ft, in
Mass g, kg, lb, oz
Volume l, ml, gal
Time s, ms, min, h, Ms
Area m2, ft2

Use the spelling your document needs; autocomplete in the editor can help find valid unit names.

Converting units

Use in, into, as, or to (case-insensitive) to convert:

10 USD in EUR
10 km in mi
123123 ms in min
100 cm in m in km

Conversions chain left to right:

100 cm in m in km    → 0.001 km

Convert a plain number by assigning the target unit:

10 in EUR    → 10 EUR

Convert a variable:

length = 20 cm
length in m    → 0.2 m

Mixing units in expressions

When you add or subtract compatible units, Compio converts automatically to a common unit (the rightmost unit with a value wins):

10 cm + 1 m    → 1.1 m
10 USD + 1 EUR → 9.65 EUR //combines in EUR (with live rate)

Multiplication and division work on the numeric parts; incompatible unit combinations produce NaN (not a number):

10 cm * 2       → 20 cm
10 cm * 2 EUR   → NaN
20 cm + 10 EUR  → NaN
10 kg + 5 m     → NaN

Ambiguous unit names

Some spellings match more than one unit. For example, MS can mean megaseconds (Ms) or milliseconds (ms). Compio reports an ambiguity error and suggests the possible units — pick the exact spelling you mean:

100 Ms     → megaseconds
100 ms     → milliseconds

Comments and headings

Comments start with // and are ignored by the calculator. Use them for notes, chapter titles, or to disable a line temporarily:

// Monthly budget
rent = 1450 EUR
// utilities = 200 EUR

Headings start with # and are also non-calculating markers for structure:

# Trip planning
flight = 642 USD

Toggle comments from the editor toolbar or with the standard comment shortcut (ctrl+/ or cmd+/ for Mac OS).

Limitations

No sync between devices. Compio has no accounts and does not upload your notebooks anywhere. Everything is saved on the device and in the browser you are using.

What that means in practice:

  • Notebooks on your laptop are not available on your phone, tablet, or another device.
  • Different browsers keep separate copies, even on the same machine.
  • Installing Compio as an app (PWA) still uses the same browser storage; installation does not back up documents elsewhere.
  • Clearing site data, uninstalling the browser, or using private browsing can remove or isolate stored documents.

Currency signs are not supported. Use ISO 4217 codes instead of symbols:

Not supported Use instead
$100 100 USD
€50 50 EUR
£20 20 GBP

Currency conversion between codes (e.g. 10 USD in EUR) requires a network connection; rates come from the Frankfurter API. But once used exchange rates are cached, it can work offline, though the rates will be outdated.

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