Enabling users to retain accuracy without returning thermal mass flowmeter to factory for gas recalibration, QuadraTherm 640i/780i with qMix™ gas mixing software let users create custom gases or gas mixtures to compensate for gas compositional changes in field. Operators can, via included software package, also create and upload unlimited gas mixtures onto meter, save custom gas mixtures onto personal My Gases Database for later use, and download accurate gases from qTherm Gas Database.