Looks like a typo re. caching values.
Allow charts to contian non-ascii.
Match existing coding style.
Removed need for explicit encoding of the file.
Add support for preserving formulae when reading.

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branch : preserve formulae on reading
Add support for preserving formulae

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branch : preserve formulae on reading
Replace naive checking for datetimes with NumberFormat

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branch : preserve formulae on reading
Test for reading formulae

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branch : preserve formulae on reading
Whitespace

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branch : preserve formulae on reading
Add test for detecting formulae when reading.

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branch : preserve formulae on reading
Completed test.

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Merge
Internal method renamed to be more explicit.
Common code from different methods refactored into single method.
Tests updated.

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branch : Charts with datetime axes
The x-axis test duplicated the y-axis. Refactored to test the underlying method only.

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branch : Charts with datetime axes
Renamed method to reflect values being used.

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branch : Charts with datetime axes
Added some comments to handling and stub tests for other data types.

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branch : Charts with datetime axes
Maintain cell data-type as long as possible.
Remove duplicate type inference from chart writer.

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branch : Charts with datetime axes
Calculating axes values for every sequence is inefficient. Added a dedicated method which is called only when the chart is written.

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branch : Charts with datetime axes
Refactored propery to use descriptor.
Added a convenience method for extracting the unformatted value (what Excel sees).

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branch : Charts with datetime axes
Documentation stub.

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branch : Charts with datetime axes