This was far more handy when calibration required more than ten battles, but it remains a little quirk that some players do not know about.
The Blitz app does not show your preliminary rating during calibration, but the data exists and is actually in the API.
Go to https://www.blitzstars.com/ and look at the top right corner above your Mastery count. You should see your current rating number as long as you've played at least one game for the season.