# Convert dates

The Convert dates module allows you to convert dates to a decimal year so that BC dates may be set with more precision than just the year. (E.G. you might be interested in modelling the Roman v Carthage campaigns).

The module uses a Gregorian calendar to provide a continuous range. (This is clearly anomalous for early dates but it is a way of easily specifying dates where the exact date may not be known but the interval between dates is known.)

If you have a layer with a string field containing dates in one of the formats shown, e.g. "-0300/08/01", and also have a suitable decimal field, then you can convert the string dates to decimal dates which can then be used by the Date control module.

The currently selected layer is entered into the Layer combo-box and its fields are loaded into the Text date field and the Decimal date field combo-boxes as appropriate.

If any records are selected then by default only these will be updated, though you may uncheck the Update only selected rows check box if you want to update all records.

Click the Update decimal dates button to do the update. You will get a message saying how many dates were updated and how many errors were found.

If you want to increment dates by a specified number of days, then set the number of days in the Days increment spin box and click the Increment dates button. The dates are incremented based on the value of the text date field but both the text dates and the decimal dates are updated.

The group box Date calculator and checker contains controls enabling you to check how the conversion works as well as providing a way of finding the decimal year equivalent for a given date and vice versa. The date may be entered by using the spinners at the top (or just typed in). This will produce a day number and decimal year. The calculated results are there so that the consistency of the dates produced can be checked.

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