Throughout this explanation I use examples of what I am talking about. They are in the spoiler tabs. If the initial explanation doesn't make sense, check the example.
First some terminology that I will use throughout:
-Weight Class: Light, Medium, Heavy, or Assault
-Chassis: The generic type of the mech. Centurion, Atlas, Commando, etc. This is the part of the designation before the hyphen as well. CN9, AS7, COM, etc.
-Variant: The specific model of a chassis. This is the part of the designation after the hyphen CN9-A, AS7-D, COM-2D. Note that there are several special releases of many mechs, such as the champion mechs (e.g. AS7-RS(c), etc.), founder's mechs (e.g. CPLT-C1(F)), phoenix mechs (e.g. LCT-1V(P)), clan invason mechs (e.g. TBR-Prime (I)), and more all the time that are considered to be the same variant as their non-champion/founders/etc. counterparts.
For clan mechs the variant is defined by the center torso omnipod. The center torso used determines where the experience points are awarded.
The pilot lab has three tiers of efficiencies for each mech: Basic, Elite, and Master.
You must own a mech in order to unlock the efficiencies, but you can gain experience by piloting either a trial mech or one that you own. You will get to keep the experience that you’ve earned, but you will not be able to apply it to any of the efficiencies until you actually purchase that variant. If you sell a mech you will keep all of your experience and unlocked efficiencies for it, should you choose to buy it again later. If you buy a second mech of the same variant as one you already have then the experience and skills will apply to both.
The XP that you earn is specific to the variant that you were piloting when you earned it, and can only be applied to the efficiencies of that variant. Any GXP that you earn can be applied to any variant of any chassis, however GXP is the only way to unlock pilot skills (modules) so it is better to save it for that instead. Once you unlock the master efficiency for any variant you will continue to earn XP for that variant (as well as GXP). The only thing that you can do with the accumulated XP is to spend MC to convert it to GXP.
The eight basic efficiencies are available for every variant as soon as you purchase it. You can unlock them in any order, and plenty has been written about which ones you should prioritize.
Once you have all eight basic efficiencies you will notice that the elite efficiencies are still locked. You will need to own three variants of that chassis, and earn all of the basic efficiencies for those in order to unlock the elite efficiencies.
Once all four elite efficiencies have been unlocked on one variant the effects of the basic skills for that variant are doubled. This is a very nice bonus that is reason enough to earn the elite skills (which are very good on their own).
In order to move past the elite efficiencies to get the master efficiency, you must first complete the elite level of three variants within the same weight class (note that they don’t have to be of the same chassis; this will be important later). Unlocking the master efficiency does not double the elite efficiencies. The tech type of the mechs (clan versus inner sphere) does not matter, only the weight class.
If you were to purchase a mech of a different weight class, you would have to do the same procedure all over again. Earn the basic efficiencies for three variants of the same chassis in order to unlock elite. Earn the elite efficiencies for three variants within the same weight class in order to unlock master.
If you purchase a new chassis of the same weight class as a chassis for which you have three variants with all of their elite skills you will have less work to do in order to reach master level. You will still need to buy three variants of that chassis and earn all of the basic skills. Once you have done that, however, you only need to earn the elite efficiencies for the ones that you intend to take to master level (because you already have three variants within that weight class with their elite skills). Remember that this works no matter whether they are clan or inner sphere mechs. Only the weight class needs to match.
It may seem confusing at first, but I hope this guide will help some of you. If you have any feedback or critiques I would be happy to hear them.
My thanks to scJazz and Padric for their contributions in another thread that led to this guide.
EDITS
Edited by Darwins Dog, 21 December 2015 - 05:34 AM.