### Display MJD values and tables

The headers and tables found in the IMB-FITS file rely heavily on time-stamps described with Modified Julian Date (MJD). This includes subscan start and stop, instantaneous antenna positions during the subscan, dump sampling during integration. These quantities can be displayed in a graphical way with e.g. the following command:

    MRTCAL> @ plot-mjd iram30m-4mhz-20100930s200-imb.fits

The result is shown in the Figure . Under normal conditions, there should be backend data and antenna positions during the whole subscan, i.e. the markers should start before and end after the box edges. It is a sane behaviour to have a bit more of data before and after the subscan limits.

Figure: Resulting plot of the procedure @ plot-mjd. X axis is time, Y axis is the subscan number. It displays i) the “on-source” time coverage of each subscan (subscan-start and subscan-stop as boxes), ii) the time coverage of the backend data in each subscan (green+gold horizontal segments), iii) the time coverage of the antenna slow positions (blue or red markers), iv) the time stamps of the derotator dumps if relevant (magenta crosses). Each DATA dump is displayed as an horizontal segment showing its actual integration time. The associated time stamp is displayed as a vertical segment (the time stamp can be found anywhere from the beginning to the end of the integration, according to the header value TSTAMPED); colors are alternated to avoid confusion.

Figure: Same as Fig. , but the backend tables are incorrect (a lot of subscans have no backend data in the subscan range).