# Error Scan Mode

xyscan provides an easy way to scan not only the data points but also the referring error bars. You can either treat the errors as asymmetric or symmetric depending on the values selected in the Error Scan Mode fields in the Settings window (see below). However, even in the symmetric case upper and lower (left and right) error bars are always scanned separately. xyscan provides different ways to derive symmetric errors from asymmetric ones.

The error scan modes are:

`No Scan`
  No error scan will be performed.
`Asymmetric`
  Lower and upper (left and right) error bars are scanned and stored separately.
`Symmetric(mean)`
  Lower and upper (left and right) error bars are scanned separately but only the average (arithmetic mean) of both is recorded. Choose this option when the error are symmetric and you want to increase the precision on the error values.
`Symmetric (max)`
  Lower and upper (left and right) error bars are scanned but only the largest of the two is stored. Choose this option when you want to play safe and especially if the image/plot is of pour quality.

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