The data are processed completely as they arrive (at 1 second intervals): images from different subarrays are combined, a mean sky level subtracted, then corrected for extinction and calibrated.

The calibrated Frame image is displayed. Creation of a new Group image is deferred until a minimum number of Frame images have been created to deal with any spikes in the Frame images. This number is set to 10 and may be changed: see the NMOS parameter for _MAKE_MOSAIC_GROUP_DESPIKE_ below. The new Group image is displayed and its noise properties are calculated and logged.

• This primitive can not handle time series data.

• The number of images to combine into a new Group image is set by the NMOS parameter for _MAKE_MOSAIC_GROUP_DESPIKE_. Smaller numbers will result in more frequent updates of the Group image at the expense of de-spiking and good variance estimation.

• The current noise level is stored in log.noise, the positions and fluxes of any sources are stored in log.flux.

The Frame image is displayed in Gaia window 1. The Group image is displayed in Gaia window 2; its variance is displayed in window 3.