Tempo ratio.

I am working on a score for ‘Chi La Gagliara’ and am having a spot of bother with tempo ratios.

Where the score goes into 6/8 time, bar 22, there is a change of tempo indicated as:

[ a = b], where
‘a’ represents a quarter note and ‘b’ represents a half note.

Can someone please explain what this means in real terms.
Does the tempo speed up or slow down by a factor of 2?


„Tan tan tan, tarira“
I guess (rather than doubling the speed) the beat stays the same: the CutC half bar equals to the half bar in the 6/8 tempo.
This is how the tempo is notated in an early print (Burney):

Hi k_b,
That’s an interesting image you’ve sent me.
Still not quite sure what to do with the ‘tempo change’.
On YouTube videos it’s a slow down. Our Conductor says that’s wrong and it should be at a faster tempo.

This is new to me. fly on the wall

Take your example where a=b, “a” being a quarter note and “b” a half note and pretend that at the beginning of the piece you set your metronome to sound on each quarter note. After the “a=b” sign, the metronome will now be sounding on each half note so two quarters or their equivalent will need to be sounded in the time previously given to only one. This might be characterized as speeding up. However, as such signs often occur where there is a change of time signature the result may sound more like a fundamental change of rhythmic character (for example, in a change from a duple rhythm like 2/4 to a compound one like 6/8) than a simple change of speed. I hope this helps.