The purpose of this document is to give the theoretical basis for algorithms used to produce all Level 3 products for those EOS MLS measurements that have sufficiently high signal-to-noise to produce useful daily maps. These products are listed in section 1.3, and will be produced using only the MLS Level 2 data files as inputs. Algorithms for producing MLS Level 3 products from the other MLS measurements, the ‘noisy’ measurements, are described in Livesey and Snyder [2004]. Those Level 3 products are produced directly from the MLS Level 1 data It should be noted that, although the algorithms described here are developed for those MLS measurements with sufficiently high signal-to-noise, they can also be used with any MLS Level 2 file as input. This provides needed flexibility for producing daily maps for MLS measurements whose signal-to-noise may be better than now expected. It also provides cross-checking of the zonal mean and monthly mean maps to be routinely produced using the other algorithms mentioned above for ‘noisy’ measurements.