Clarification needed in `_pd_meas.rocking_angle` description

[rowlesmr]

_pd_meas.rocking_angle is currently described as

The angular range in degrees through which a specimen is rotated or oscillated during a measurement step (see _pd_meas.rocking_axis).

To me, "rocking" means going back and forth, so "oscillated" is correct, and "rotated" is not entirely correct. Additionally, if the value is 5, does/should this mean ±5° or ±2.5°?

[rowlesmr]

This could also be used to record that you are spinning a sample in a Bregg-Brentano measumrent.

_pd_meas.rocking_angle  180
_pd_meas.rocking_axis     phi

[jamesrhester]

I think the intention is that 5 degrees is 5 degrees total. In the case of a Debye-Scherrer sample, the sample could indeed oscillate back and forth if the equipment is not up to free rotation. This quantity is useful to give a guide to the total amount of angular space covered by the measurement. Are you thinking there is a reason to distinguish between rotation and oscillation?

[rowlesmr]

I was thinking that in a situation like rocking the specimen in omega, when collecting data in 2theta. The rocking should be centred on the collection angle, as opposed to being at one end.

Could be enhanced with some extra explanation, and maybe an example

The total angular range in degrees through which a specimen is rotated or oscillated during a measurement step (see _pd_meas.rocking_axis). Where the rocking axis aligns with a measurement axis, the total angular range is assumed to be centred on the measurement point.

_pd_meas.rocking_angle   5
_pd_meas.rocking_axis    omega

_pd_meas.2theta
_pd_meas.counts
12.00  123
12.02  124
#...

Specimen is rocked +- 2.5 deg about the measurement points 12.00 and 12.02 deg 2Th.

_pd_meas.rocking_angle   180
_pd_meas.rocking_axis    phi

_pd_meas.2theta
_pd_meas.counts
12.00  123
12.02  124
#...

Specimen is rotated 180 degrees during the collection of the data at 12.00 and 12.02 deg 2Th

[jamesrhester]

Sounds reasonable. The only issue would be if there are situations where you want to rock and not be centred on the measurement point, but that could be handled later by defining a new data name if it comes up. Debye-Scherrer geometry is not really excluded by the definition - the measurement axis does align with the rocking axis, but the rotation range does not relate to the point being measured.

[rowlesmr]

the measurement axis does align with the rocking axis, but the rotation range does not relate to the point being measured.

I can add that to the description.