Cervelo Dual 9 Cassette

I am a newbie and I have a Dual 9 that I bought from my local Tri Shop earlier this year. I do not have much of a biking background, at least not with fixing or tinkering to much although I am doing more and more…

My question is that I am getting a set of slightly used Race wheels without a Cassette. I am not sure what Cassette I have on my bike. I don’t see numbers and instead of counting I thought I would ask if anyone knows what the Standard is on the Ultegra 9 that comes with the Dual. (Pretty lazy I admit) I may get a Cassette from my local bike shop 5 miles away vs my “local” tri shop 50 miles a way.

Thanks

I am pretty sure each of the cogs has a small number etched into it that gives you the number of teeth in that cog.

EG, my Dual 9 goes from 12 - 23…never bothered to work out what is in between these two.