For today's Advent calendar entry, we see what happens when you play the wrong take of a current affairs show.

The 18th window of the CVTNAC springs open to reveal this floor plan of studio G at Lime Grove, the compact complex occupied by BBC Television from 1950 to 1991. Over the years, G was home to shows like Dee Time and Top of the Pops, but its rectangular shape made it less ideal for situation comedies. The first Hancock's Half Hour TV series was made here, but the various sets had to be placed in a line along one wall, with the audience a few seats deep along the other, with a majority of audience members unable to see what was going on at any given time. It was never converted to colour and closed in the very early 1970s.

A Pye mark 4 advert for the 17th day of Advent.

Tuesday's Advent calendar window pops open to reveal a coaster advertising HTV's studio and post-production facilities. The north Wales facility was reputedly very little used as news editors hated stories that were covered in Mold. Ay theng yew.

A double bill for today, as I was unable to get to a computer on Sunday. First off, the electronic test card known to its friends and associates as PM5544. Check your gratings. Go on. Fiddle with your colour, brightness and contrast until everything looks just right. It's all good, and it's all for you.

Secondly, the final credit from the BBC's 1972 adaptation of Hedda Gabler, complete with copyright date added as an afterthought, as this was the transitional era between shows ending with a simple BBC tv (up to late 1971, if memory serves), BBC Colour (late 1971-early 1972) and displaying a date. Roman numerals were adopted from 1977 onwards, apparently to disguise the age of some of the repeats.