Hello. This is my first post on this forum.
I bought Starcraft back in 98, but I have recently started playing again. I have noticed dramatic increases in my decision-making and APM since I started about two months ago. I'm not a pro, by any means (currently a D on ICCUP, with a little over 50% win ratio, half-way to D+, and my B.Net stats are similar), but I do enjoy playing Starcraft.
One thing that bugged me was trying to figure out how many SCVs to use (I play Terran) for their maximum return on investment. If I was only concerned with efficiency, I would use only 1 per mineral patch, and if I was only concerned on the speed of mining, I would use 3+ per patch (maybe more).
I wanted to determine what the best rate mining was for the minimum input. For this, I needed to run a few trials.
I tested this on a number of different maps, with a variety of numbers of SCVs. I tested with 1.0, 1.3, 1.6, 1.9, 2.2, 2.5, 2.8, and 3.1 scvs per patch.
The results I obtained were interesting. They were different than I expected, which is why I wanted to share this.
1.0 scvs/patch mined 59 minerals/scv per minute.
1.3 scvs/patch mined 54 minerals/scv per minute.
1.6 scvs/patch mined 50 minerals/scv per minute.
1.9 scvs/patch mined 47 minerals/scv per minute.
2.2 scvs/patch mined 45 minerals/scv per minute.
2.5 scvs/patch mined 43 minerals/scv per minute.
2.8 scvs/patch mined 41 minerals/scv per minute.
3.1 scvs/patch mined 41 minerals/scv per minute.
I ran 8 trials of each, and these are heavily rounded averages. I used the more precise numbers in the calculations later on.
Now, that is how fast they return minerals. Note: about 3 scvs/patch mines approximately double what 1.0 scvs/patch mines. To determine what is really best, the cost of the scvs, plus appropriate Supply Depots and the Command Centre must be taken into consideration.
Assuming 9 patches of minerals (which is very common on most currently popular maps (excluding fastest, which I do not like playing)), the costs of mining with said number of scvs is
1.0 scvs/patch is 838 minerals
1.3 scvs/patch is 1025 minerals
1.6 scvs/patch is 1150 minerals
1.9 scvs/patch is 1338 minerals
2.2 scvs/patch is 1525 minerals
2.5 scvs/patch is 1713 minerals
2.8 scvs/patch is 1838 minerals
3.1 scvs/patch is 2025 minerals
Now, you may think I'm nuts with these calculations, but I've taken into consideration that there is a supply cost to having this many scvs, as well as the cost of the command centre. Although you do not pay for the first one, IMO it is more important knowing how much an expansion will cost.
Now, comparing the rate of mining compared to the cost, it comes out as follows
1.0 scvs/patch returns 63% of its cost per minute
1.3 scvs/patch returns 63% of its cost per minute
1.6 scvs/patch returns 61% of its cost per minute
1.9 scvs/patch returns 60% of its cost per minute
2.2 scvs/patch returns 59% of its cost per minute
2.5 scvs/patch returns 58% of its cost per minute
2.8 scvs/patch returns 58% of its cost per minute
3.1 scvs/patch returns 57% of its cost per minute
This is where I thought it would be different. They are all very similar. I thought there would actually be a peak somewhere around 2.5, which is why most people argue that it is the best.
Now, considering a real-game situation:
If your opponant has his main and natural, and his mineral line is saturated (3+ workers/patch), that is a huge investment. To get roughly the same rate of mining as your opponant has, you need to have your main, natural, and 2 more expansions with 1.0 scvs/patch.
Multiple bases have some benefits, such as more space, better map control, etc. Also, if you are harassed, it does not hurt your economy as badly as if you had all of your workers in a smaller area. This also frees up your max supply better (ie. you use 40 scv, your opponant uses 60), so you can have a larger army in total. You also have the ability to make twice as many comsat/nuclear silos (for those who actually make them.....) as your opponant. You can also produce workers at twice the rate of your opponant (yes, Zerg is different, but a similar principle applies to them too, they have a maximum rate of building units in total, instead of just workers).
The main downside I see is that you are more open to attacks, because you have to spread yourself out more. Unless you can somehow contain your opponant, you will be at their mercy.
So, because of this, I believe there must be a medium somewhere. Only mining out of two bases at a time hurts in some ways, but it is easier to defend. Mining out of more bases gives you a better economy for a lower cost, and allows you to build a bigger army but you are more spread out.
Maybe this is why that "2.5 workers/mineral patch" is a rule of thumb. It is somewhere inbetween. Also, 2.5 scvs/patch allows you to transfer a few workers to a newly made expansion without hurting your current economy. That is a huge benefit.
It appears that between 2 and 2.5 workers/patch is actually ideal. It has benefits, and drawbacks compared to either extreme, but it is not as severe. Instead of continuing scv production after 2.5, you should start another CC (if you haven't already, and you probably should have).
This information also means - if you get a good containment on your opponant, FLAUNT IT. Go out and build another command centre (or 2, 3, 4+) if you can, and have only 1 scvs/patch mining. If they break containment, you've still probably had an excellent return on investment (it only takes about 100 seconds of mining at each one to pay for itself, anything after that is helping your economy in a huge way).
I've played a couple of long macro games, where this kind of mentality has either won or lost the game for me. Now I know why.
Anyways, I thought I would share this revelation with some other SC players.
As a side note - why is there no love for the Wraith? I love that unit. It is an awesome sniper unit. I typically use 6-10 every game, for economy/supply harassment, and sniping dropships, science vessels, overlords, guardians, shuttles, carriers, battlecruisers, reavers, sieged tanks, arbiters, etc..... They are so useful as snipers, to run in, hit something scary, then retreat. Is this impractical in higher levels of play?