Do I still need the CIRC Breaker with modern Excels?

So I am currently prepping my modelling skills to transfer from MBB to banking

What I always wondered: I used to watch some very old modelling videos were they always have been super adamant about the circ-breaker ("if you forget this your model won't work, will break down, etc."). 

Now in the newest versions of excels my LBOs always worked perfectly fine without building out a circ switch (due to "iterative calculations" being enabled). 

I am wondering if I still could face a potential blow-up? In consulting I am used to work with onedrive so anyway I consistently have my model saved and even if smth blows up I just go to the version of 10min before.

3 Comments
 

Iterative calculations don’t bypass the need for a circ switch — in fact, it doesn’t really make sense to have a circ switch without iterative calculations, as the latter is only needed because your logic is circular.

Whenever you have circularity, you run the risk of cascading errors because A is dependent on B which is dependent on C which is then in turn dependent on A etc.etc. Furthermore, since there are these circular dependencies, error fixing can be quite difficult — hence the need for a circ switch that you can toggle to kill the circular logic and break the loop of errors.

 

Ya lol the whole point of the circ is because of iterative calculations. When you build in this loop, it makes the model inherently unstable and if you have a couple at play (eg option dillution etc , see some of the later peak framework models), it can get quite unstable and glitch out. 

Though you make an interesting point— I do wonder if there will be a day where you don’t need the circ switch. I THINK it’s less about excel and more about the processing power of your computer but because the instability is always going to be there from the way you have to calculate these things, I imagine it’s always going to be needed 

 

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