To sum values in a document, open a collection and tap on button → Select Fields.
You should create two decimal number fields such as Amount 1 and Amount 2.
![Sum values](/img/screen/sum-document/sum-fields-list.png)
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Tap on Edit.
![Sum values](/img/screen/sum-document/sum-formula-field.png)
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Add a Formula field with the button.
![Sum values](/img/screen/sum-document/sum-decimal.png)
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Select Decimal number.
![Sum values](/img/screen/sum-document/sum-fields-done.png)
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Tap on Done.
![Sum values](/img/screen/sum-document/sum-open-field.png)
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Open the newly created field.
![Sum values](/img/screen/sum-document/sum-edit-formula.png)
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Assign a name such as Sum and tap on Edit formula.
![Sum values](/img/screen/sum-document/sum-formula-1.png)
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The formula is empty. Tap on the button to add an expression.
![Sum values](/img/screen/sum-document/sum-formula-function.png)
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Scroll down and select the Sum function.
![Sum values](/img/screen/sum-document/sum-formula-function-plus.png)
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Tap on the button again.
![Sum values](/img/screen/sum-document/sum-amount-1.png)
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Select Amount 1 (or another field) from the list.
![Sum values](/img/screen/sum-document/sum-amount-2.png)
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Tap on button and repeat the previous step selecting Amount 2 (or another field).
![Sum values](/img/screen/sum-document/sum-done.png)
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The formula is completed, tap on Save to confirm.
Subctract values
To subctract values (difference between values) you can use use the Minus function. The Minus function prepends a minus in front of a number.
![Subctract values](/img/screen/sum-document/minus-function-example.png)
The example shows how to use the Minus function.