So! Let us say that you have a Focus Token, and 3 attack dice.
Your possible rolls are: CCC, CCH, CCF, CCB, CHH, CHF, CHB, CFF, CFB, CBB, HHH, HHF, HHB, HFF, HFB, HBB, FFF, FFB, FBB, and BBB, where C is the hollow explody, H is the solid explody, F is the Eyeball, and B has no symbol.
For each of these, you can calculate the odds of them by multiplying the odds of the individual results together, then multiplying the amount of different ways you can order the results.
All of the following are the numerators to the fractional results: the denominator being 8^3, or 512
CCC = 1*1*1, *1, or 1
CCH = 1*1*3, *3, or 9
CCF = 1*1*2, *3, or 6
...
CHF = 1*3*2, *6, or 36
Et cetera et cetera.
Now then, the question becomes this: When is Calculation great?
When you only have only one F result, and still intend to spend your Focus Token on the attack, and aren't facing a fleet against whom Crits are a bad idea.
That is, the CCF, CHF, CFB, HHF, HFB, and FBB results, and not fighting against a ship with Determination, Leebo, or near ships with Draw Their Fire.
1*1*2*1 + 1*3*2*6 + 1*2*2*6 + 3*3*2*3 + 3*2*2*6 + 2*2*2*3 = 212, out of the 512 possible result combinations, or 53/128 for the fully reduced form (or appx 41%).
A minor improvement of the action that procs appx 41% of the time? That's definitely worth 1 point, particularly on Crit-lovers!
Now, the other comparison: How often is Calculation better than Marksmanship?
Well, with the above situations, it is strictly better as it costs 2 points less,
Moreover, when you have rolled more than one F result, you have reduced your damage only by one Crit-to-Hit conversion, as it's still a Focus token.
Additionally, in every situation in which you haven't rolled any Focus results at all, this is strictly better as your Focus token can be spent defensively, and therefore haven't wasted your action.
Marksmanship is therefore only superior to Calculation in the instances in which you get multiple attacks in a round, cannot use Focus tokens for some reason, or have rolled multiple Focus results.
The multiple Focus results are: CFF, HFF, FFF, and BFF, which are 1*2*2*3, 3*2*2*3, 2*2*2*1, and 2*2*2*3 respectively, or 80/512, meaning that it's only an improvement 5/32 of the time, and then only by one hit-to-crit conversion, on most ships. That is not worth two additional points!
A minor improvement that procs 5/32 of the time is not worth an additional 2 points. Still, it is better when you get multiple attacks in a round (Corran Horn, Gunner/Crew Skywalker), so Marksmanship is not entirely dead.
That being said, I would typically prefer to keep my Focus token for defense if I only got 1 or fewer F results, or spend it without using Calculation if I had more than one.
This card is great on mid-level pilots, as you'll have already spent your focus defensively by the time you get to shoot, and on the crit-lovers (Ten, Kath, Maarek, and I'm sure I'm forgetting at least one). It's also good on anyone who generates multiple focii (Whisper, Moldy Crow, Recon Spec, Garven Dreis, Kyle Katarn, et c.), or anyone who doesn't rely on Focii for damage mitigation (pilots with Agility of 1 or fewer, Luke Skywalker).
