Calculating preferred share conversions to common using weighted average

I am trying to make an informed decision as to whether or not to invest in a private startup company by exercising vested options from a grant I obtained while working for the company as an employee.

In reading their corporate filings I have discovered that the preferred share class have the following liquidation preferences:

1. 1x return of original purchase price OR
2. conversion to common shares using a weighted average price calculation (anti-dilution protection) so they can participate.

The preferred shares are ranked pari passu across the series of funding.

The formula they use for the conversion price of a preferred share is the standard broad based weighted average:

``````CP2 = CP1 x (A + B) ÷ (A + C)
``````

The startup has raised 4 series of funding as follows:

``````Series A-1
Series A-2
Series B
Series C
``````

Question: My biggest unknown is whether I would calculated this broad based weighted average in one step for each series of preferred shares, or if I have to repeat the calculation between every series of funding. For example if I'm calculating the A-1 preferred shares conversion do I have to calculate: A-1 -> A-2, A-2 -> B, B -> C? Or just A-1 -> C?