So far it was always hard to find the correct calibration files for a given observation. With today's changes, this will be a lot easier! :-)
First, remember that observation IDs (e.g. on the Status page or the Status tab of a task) are always links, e.g.:
The link always takes you to the info page for the observation with download links, weather infos and more. From now on, we also present links to available calibration observations:
The system shows you separate groups for BIAS, DARK and FLATFIELD observations. Clicking on the title shows a list of available calibration observations. They are picked in a way that they have the same binning as the observation, the same or larger exposure time (for DARK frames) and same filter (for FLATFIELDs). For each parameter combination, it shows you five results closest in time to your observation. So for example, if you observed in two filters, you get up to 10 links (5 for each filter) to FLATFIELD observations.
The observation ID in the first column is of course again a link to the observation's info page and the button in the last column lets you download the master calibration (median of all frames) directly.
The info shown depends on the kind of observation you're looking at. So within a BIAS observation you never see links to other BIAS or DARK observations. But for all calibration observations you'll see an additional group "Reduced master calibration file", which allows you to download the final calibration master.