One of the most common applications of SDDS for APS commissioning and
operation is logging of measured data values at intervals. A set of
generic EPICS monitoring programs `sddsmonitor`, `sddsvmonitor`
(vector monitoring), and `sddswmonitor` (waveform monitoring) are used
for this. One example is the vacuum pressure in the APS ring, which is
logged continuously by `sddsvmonitor`; this data consists of readings
from ion gauges around the ring. Another example is logging of
beam-position-monitor readouts in the Positron Accumulator Ring (PAR) and
its input and output beam transport lines using the program `sddsmonitor`.

For use in examples, I'll assume the existence of two files called `SR.vac` and `par.bpm`. These are simplified from actual files
collected with the programs just mentioned.

`SR.vac` is a file containing an arbitrary series of data pages, each
consisting of a snapshot of the vacuum gauge readings around the ring.
There are 40 such readings, one for each sector of the accelerator.
Typically, one set of readings is taken every 15 minutes.

- Parameters:
`TimeStamp`-- A string parameter containing the time at which the snapshot was taken.`TimeOfDay`-- A double-precision parameter containing the time of day in hours since midnight.

- Columns:
`Index`-- A long-integer column containing the row index.`SectorName`-- A string column containing the name of the sector each row corresponds to.`Pressure`-- A double-precision column containing the pressure readout from the gauges at the time given by`TimeStamp`.

`par.bpm` is a file containing a single page of data with any arbitrary
number of rows. The PAR has 16 beam-position-monitors (BPMs), each
providing a horizontal (x) and vertical (y) readout. In addition, the beam
transport line downstream of PAR (known as the PTB line), contains five
BPMs for x and five for y. The data included in the distribution contains
only the x values, since these are more interesting:

- Parameters:
`TimeStamp`-- A string parameter giving the starting time of the data collection.

- Columns:
`Time`

-- A double-precision column giving the elapsed number of seconds since monitoring begain. The values are approximately equispaced.`TimeOfDay`

-- A double-precision column giving the time of day in hours since midnight.`P`

*quadrant*`P`

*number*`x`

-- 16 single-precision readouts of the horizontal beam orbit just prior to beam extraction.*quadrant*ranges from 1 to 4, as does*number*.`P`

*quadrant*`P`

*number*`y`

-- 16 single-precision readouts of the vertical beam orbit just prior to beam extraction.*quadrant*ranges from 1 to 4, as does*number*.`PTB:PH`

*number*`x`

-- four single-precision readouts of the horizontal beam trajectory as the beam passes through the PTB transfer line.*number*ranges from 2 to 5.