Basic Examples (2) 

Refer to an object that took substantial resources to compute:

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Use a graphical object that typically slows down the user interface when interacted with (e.g. over a slow remote connection):

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Scope (1) 

Refer to an expression not immediately previous to the current one:

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Options (1) 

Ignore text cells when counting:

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Possible Issues (4) 

Text cells do not evaluate if their contents are not evaluable:

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Referring to the input cell of an input-output cell group reevaluates the input, leading to repeated computations:

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Refer to the generated output cell instead, which is not evaluated any further:

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If n refers to a nonexistent cell, a ToExpression::notstrbox is produced:

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If the cell being referred to contains an evaluable instance of EvaluatePreviousCell, recursion errors may occur:

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Avoid reevaluating EvaluatePreviousCell by matching only output cells:

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Neat Examples (1) 

Use the binary representation of expressions to store and retrieve persistent data within the notebook:

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