replace tau with more universally accepted name

[ambarb]

to be updated next week....

[prjemian]

sneak peek from today's discussion:

[JulReinhardt]

@ambarb Which name for tau did we decide on eventually?

[ambarb]

so a quick literature/internet search produced some information.

I thinks "delay" is the experimentalists' term because they had to add an electronic delay to the data collection circuit back in the 50s. From a statistics point of view, the word "lag" is used. I think both are technically correct. I know the APS really likes delay so maybe we can go with delay_step but include in the description for this:

"delay (or lag) is the quantized difference so that the "step" between 2 frames is 1 (or step = dt = 1 frame). Units of frames (i.e., integers) are the standard as we have two different independent confirmations that integers handling scales best for future data wrangling plans. This file requires usage of NXdetector to define the time step conversion (NXdetector XXXXX)"

@prjemian I cannot seem to find the field name for what is in EPICs cam.acquire_period. I know suresh thought that it wouldn't necessarily be epics that contains this information for all cameras, but we need a common place to put this.

Also, @prjemian can you agree "delay" is a word we should be using: NXdetector has used "delay" but it seems in a different context.

[prjemian]

field name: ad_object.cam.acquire_period.pvname I believe AcquirePeriod_RBV

"step" still seems like jargon, so perhaps adding time difference to the description, as in:

"delay (or lag) is the quantized difference so that the time difference ("step") between 2 frames is 1 (or step = dt = 1 frame).

[prjemian]

confirming the PV name with area detector ad: from the bash shell command line:

(base) prjemian@zap:~/Documents/build$ caget ad:cam1:AcquirePeriod
ad:cam1:AcquirePeriod          0.005
(base) prjemian@zap:~/Documents/build$ caget ad:cam1:AcquirePeriod_RBV
ad:cam1:AcquirePeriod_RBV      0.005

and from the bluesky IPython shell:

In [1]: adsimdet.cam.acquire_period.pvname
Out[1]: 'ad:cam1:AcquirePeriod_RBV'

[prjemian]

But you were asking for the field name we us in NXxpcs? NeXus has only one such use, in NXsource as period. Our use is different. Suggest adding acquire_period our use of NXdetector.

[ambarb]

refreshing our memory, we know that we decided:

tau --> delay_difference

see #57 for decision making process.

[JulReinhardt]

this should be done too. Changes to delay_difference are commited. PR is in review.