I see a lot of questions on the Consortium Forums and on reddit where people ask how to tell if x profession or y profession is "profitable". In my opinion, one of the keys of an excellent gold maker is the ability to evaluate this information on the fly with some simple calculation rather than using a spreadsheet or tool (such as TSM) constantly. Know your math.
How I Do My Math
There are other ways of doing this, such as using addons and spreadsheets, but at a base level, I want to understand my product, and be able to purchase Ghost Iron Ore without using TSM to evaluate it, or a spreadsheet every time, being confident that I'm profiting at those prices. Now, no basic calculation will be perfect, but you have to trust that your theories are correct and there will be profits. Now for some examples.
I've used this example many times before, so if you've heard it already feel free to skip to the next subheading. For prospecting we know some simple rates. On average a stack of Ghost Iron will net you 1 rare and 6 uncommon gems, as well as some fraction of a Serpent's Eye. While the Serpent's Eye isn't negligible, I tend to ignore it for my simple calculations. How about those uncommons? The 6 uncommons will net you at a MINIMUM, 16g profit (2x jewelry that vendors for 9g each, and takes a 1g setting to make). Therefore an average rare gem (ie. each gem color) based on prospecting will cost you AT MOST:
Ghost Iron Ore Stack Price - 16g
For Milling, it's much a similar process, but there's actually 2 ways you can think about milling. I prefer the Starlight Ink method, but you can do it in other ways as well.
First a stack of normal (non-Fool's Cap) herbs will net you 5 Ink of Dreams and .5 Starlight Ink. Now that's 1/6th of a shoulder enchant and 1.6667 Glyphs. Kind of annoying to think about in that context, so I prefer to consider had I converted the Ink of Dreams to Starlight, it would be 1/3rd of a shoulder enchant. Since 1/6th of a shoulder enchant (in general) tends to be less than the 1.66667 glyphs, if you use the 1/3rd of a shoulder enchant calculation, you'll tend to end up with the easier calculation. For example if a stack of Green Tea Leaf is 20g, and shoulder enchants are going for 120g, you're doubling your investment if you turn that stack of herbs into a shoulder enchant (1/3rd = 40g).
Fool's Cap is 1 Starlight Ink and 6 Ink of Dreams. That's 1/3rd of a shoulder enchant and 2 glyphs or roughly one half (technically 8/15ths) of a shoulder enchant.
Knowing your mat conversions is key, and the ability to do some simple math instead of dealing with TSM can definitely speed up your buying process. For a basic example, 2 Ghost Iron Ore -> Ghost Iron Bars. A 2 to 1 ratio, so you're willing to pay twice for a bar that you would for ore. A search in TSM Shopping such as:
Ghost Iron Ore; Ghost Iron Bar
will show you both in the same window, and allow you to buy quickly and effectively. I do a similar search with Alchemy ( Ghost Iron Bar; Trillium Bar; Living Steel/exact )
Because of the proc rates, these are some of the more difficult calculations, at least some of them, while others can be quite easy. For Example 10 Ghost Iron Bars can be converted to 1 Trillium Bar. Easy enough right? BUT with xmute master 10 Ghost Iron Bars become 1.2 Trillium Bars on average, simplifying to a 8.33333 GIB to 1 Trillium Bar rate. Not the easiest calculation to do in your head. On the other hand 6 Trillium Bars will make 1.2 Living Steel as a Transmute Master. This simplifies nicely to a 5:1 ratio, very nice. So if 5 Trillium Bars < 1 Living Steel, use that cooldown! The same applies to Primal Diamonds, but I'm going to dive into that case more in depth.
For Primal Diamonds using Alchemy, I use the minimum I talked about above to estimate rather than a static cost. It takes 6 rare gems to make 1.2 Primal Diamonds, so again it's a 5:1 ratio when simplified. To quickly estimate the cost of a generic "rare gem" I just take the price of 1 Golden Lotus, add 3g (the value of an uncommon gem at a minimum in the JC scenario above), and divide by 1.2. Now that dividing by 1.2 part may seem a little tricky, but I usually just estimate that discount as ~8-10g. For example if GL=40g, Uncommon=3g:
One Rare gem = 40+3-8= 35g per gem (actual would be 43/1.2 = 35.8333333g, a fairly accurate estimate)
Primal Diamond = 35*5 = 30*5 + 5*5 = 150 + 25 = 175g/Primal Diamond
Just the Tip of the Iceberg
Now you can set up TSM to do these calculation for you, but to me I'd rather use these estimates to purchase when GL is cheap, or when herbs are at a certain price, than constantly have TSM evaluate the pros/cons at crafting at a specific point in time. On top of this, being familiar with your product, and knowing these thresholds of profitability are key for purchasing in bulk prior to needing the materials. Zerohour did an excellent piece about this, and I highly suggest that you read it.
Rarely if ever do serious gold makers buy the mats as they need them. Doing so increases your risk and leaves you hostage to the current Auction House, and whatever the prices decided to do on that particular day. Knowing your materials, and the prices that they're profitable at, can help you buy in bulk and set up searches for you to make sure you're truely optimizing profit, without using spreadsheets on the daily. That's not to say they're not useful tools, but to me they become less meaningful once you have a thorough understanding of your markets. Just knowing the relationship between mats and products will help you greatly in the long run.