What counts as a number
A number is a run of the digits 0 to 9. It may start with a minus or plus sign, include thousands separators, and end in a decimal part, so -1,234,567.89 is one number. Digits next to letters count: the 3 in 3kg and the 101 in Room101 are found. Only the digits 0 to 9 are read, so digits from other scripts, such as Arabic-Indic or full-width digits, are not found.
Scientific notation is one number when it stands on its own: 6.022e23 and 1.5E-3 are found whole and counted in the sum. Next to letters or other digits, an e is only a letter, so the code SKU12E4 gives 12 and 4. A decimal can start with the point, so .5 is 0.5, and a minus sign can be the true minus sign (U+2212) as well as the hyphen.
A minus sign is part of a number only when it is not directly after a letter or digit. That is why -5 is minus five, while the hyphen in 10-20 or 2024-05-12 is a separator, and gives the numbers 10 and 20, or 2024, 05 and 12. Plain numbers drops the leading zero of 05.
Currency symbols and percent signs are not part of the number: $19.99 gives 19.99 and 45% gives 45.
Thousands separators and decimal commas
Different countries write 1,234 and 1.234 differently, so the tool has a rule for the cases that could mean either. A comma followed by exactly three digits is read as a thousands separator, so 1,234 is 1234. A point is read as a decimal point, so 1.234 is 1.234. A comma followed by one, two or four or more digits is a decimal comma, so 3,5 is 3.5.
When a number has both, the last one is the decimal separator: 1.234.567,89 and 1,234,567.89 are both 1234567.89. Numbers with spaces as separators, such as 12 345, are read as two numbers, and Indian grouping such as 1,00,000 is not read as one.
The same rules apply to a list written with commas and no spaces, so check lists like that. 10,20,30 is read as 10,20 (a decimal comma) and 30, and 100,200,300 is one number, 100200300. Put a space after each comma, as in 10, 20, 30, to get separate numbers.
The summary
The sum, average, median, smallest and largest are worked out on every number found, in plain form and before duplicates are removed, so a figure that appears twice is counted twice. Rounding is limited to 12 significant digits, so adding 0.1 and 0.2 gives 0.3 and not 0.30000000000000004.
If a text mixes figures that mean different things, such as phone numbers, dates and prices, the summary adds them all together. Cut the text down to the part you mean, or use the list rather than the summary.