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+# Instrument
+This file defines the content of the NXinstrument group of the scan file (hdf5).
+It is a json object with as many entries as needed. One group is made inside the NXinstrument group per entry of this settings file, with the key used as group name.
+
+See source:trunk/PixelatorController/config/instrument.json for an example.
+
+### NeXus class
+Every top level entry may have a "class" member that is used as the NeXus class of the group.
+Without the "class" member, the NeXus class of the group is built using the groups name: "NX" + lower(name) 
+
+Values can be
+* strings
+* numbers
+* [positioner values](#positioner-values)
+* arrays of numbers or [positioner values](#positioner-values)
+* [value with unit](#value-with-unit)
+* objects:
+   * a nested NeXus group is created
+   * these nested objects must have a "class" member
+
+### Conditional Writing
+A group may be written conditionally. When a settings object has a "condition" member, its value defines a condition
+that must be met in order to write the entire group. The value of the condition has the form:<BR>
+`{"operator" : [values]}`
+
+values can be
+* strings
+* numbers
+* [positioner values](#positioner-values)
+* [epics channel values](#epics-channel-values )
+
+Only one operator is implemented so far:<BR>
+`{"==" : [value1, value2]}`
+
+### Positioner Values
+To write the (numeric) value of a positioner to the NXinstrument section or to use it in a [condition](#conditional-writing),
+a value can be a json object with the following members:
+* positioner: Name of a [Positioner](#positioner)
+* factor (optional): float value. The positioners value is multiplied with this factor.
+* offset (optional): float value. The positioners value is added to this offset.
+
+### Epics Channel Values
+To use the (string) value of an epics channel in a [condition](#conditional-writing),
+a value can be a json object with the following member:
+* epicsChannel: Address of an EPICS channel
+
+### Value with Unit
+As all numeric values should be written with a unit,
+a value can be a json object with value and unit:<BR>
+`{"value" : value, "unit" : unit}`
+
+value can be
+* numbers
+* arrays of numbers
+
+unit must be a string
+