# 3.1.28. Syserr: systematic errors¶

## 3.1.28.1. Overview¶

This command calculates a new error, adding the systematic error of the source and the background to the Poissonian error in quadrature. One must specify both the systematic error as a fraction of the source spectrum as well as of the subtracted background spectrum. The total of these fractions can either be less or greater than 1.

Warning

This command mixes two fundamentally different types of errors: statistical (random fluctuations) and systematic (offset). The resulting uncertainties are unjustly treated as being statistical, which can lead to wrong results when the systematic offsets are substantial. Syserr should therefore be used with extreme caution.

Warning

One should first rebin the data, before running syserr. Run syserr however before fitting the data or finding errors on the fit.

Warning

Running syserr multiple times will increase the error every time. If the input to syserr is wrong one should restart SPEX and rerun syserr with the correct values to calculate the total error correctly.

## 3.1.28.2. Syntax¶

The following syntax rules apply:

`syserr #i: #r1 #r2`

: The shortest version of this command. #i: is
the range in data channels for which the systematic error is to be
calculated and added (in quadrature) to the Poissonian error. #r1 is
then the the relative systematic error due to the source and #r2 the
relative systematic error due to the background.`syserr [instrument #i1:] [region #i2:] #i3: #r1 #r2`

: In this
syntax one can also specify the instrument and the region one wants to
calculate the combined error for. Both can be ranges as well. #i3: has
the same role as #i: in the above command, and #r1 and #r2 are the
same as above.`syserr [instrument #i1:] [region #i2:] #i3: #r1 #r2 [unit #a]`

:
Exact same command as above, except that now the data range (#i3:) for
which the errors are to be calculated are given in units different
than data channels. These units can be Å (ang), eV (ev), keV (kev),
Rydbergs (ryd), Joules (j), Hertz (hz) and nanometers (nm). This is
the most general command.## 3.1.28.3. Examples¶

`syserr 1:100000 0.3 0.5`

: Calculates the combined Poissonian and
systematic error for data channels 1:100000, where the fraction of the
systematic error of the source is 0.3 and the background is 0.5.`syserr 0:2000 0.3 0.5 unit ev`

: The same as the above command,
expect that now the error calculation is performed between 0 and 2000
eV instead of data channels.`syserr instrument 2 region 1 0:2000 0.3 0.5 unit ev`

: The same as
the above command, but now the error calculation is only performed for
the data set from the second instrument and the first region thereof.