fix PDF build

contributed_definitions/NXstress.nxdl.xml

@@ -245,7 +245,7 @@
  </field>
  <field name="wavelength" type="NX_FLOAT" optional="true">
  <doc>
- In case of monochromatic radiation, the wavelength used during the experiment. The wavelength should be provided in \ :math:`\unicode{x212B}`, but if chosen otherwise, the units must be clearly specified.
+ In case of monochromatic radiation, the wavelength used during the experiment. The wavelength should be provided in \ :math:`Å`, but if chosen otherwise, the units must be clearly specified.
  </doc>
  </field>
  </group>
@@ -1007,11 +1007,11 @@
  It defines the *cUnit* as follows
 
  - if *center_type="two-theta"* then *cUnit* must have the angle unit *degrees*
- - if *center_type="energy"* then *cUnit* must have the energy unit *keV*
- - if *center_type="momentum-transfer"* then *cUnit* must have the energy unit \ :math:`\unicode{x212B}^{-1}`
- - if *center_type="d-spacing"* then *cUnit* must have the energy unit \ :math:`\unicode{x212B}`
+ - if *center_type="energy"* then *cUnit* must have the unit *keV*
+ - if *center_type="momentum-transfer"* then *cUnit* must have the unit \ :math:`Å^{-1}`
+ - if *center_type="d-spacing"* then *cUnit* must have the unit \ :math:`Å`
  - if *center_type="channel"* then *cUnit* must be *dimensioness*
- - if *center_type="time-of-flight"* then *cUnit* must have the time-of-flight unit \ :math:`\mu\mathrm{s}`
+ - if *center_type="time-of-flight"* then *cUnit* must have the unit \ :math:`\mu\mathrm{s}`
  </doc>
  <enumeration>
  <item value="two-theta" />