* table
#+name: measurements
|       Date | PSA |         |
|------------+-----+---------|
| 2017-08-11 | 185 |         |
| 2017-08-21 |     | #ffdd99 |
| 2017-09-19 | 854 | #ffdd99 |

#+begin_src gnuplot :var data=measurements :file timeseries.pdf :results file
  set xdata time
  set timefmt "%Y-%m-%d"
  set xrange ["2017-08-01":"2017-10-01"]
  unset key
  plot data using 1:2 with histeps
#+end_src

#+results:
[[file:timeseries.pdf]]