This achievement is unlocked when you acquire 80% of unit data. You can view your progress by pressing the menu
button and tabbing to Intel. Under intel, select Unit data and you will see your progress. You can also look at specific unit data. Unit data is divided into a dozen categories. There are standard machines; machines specific to each of the five main regions; enhanced, EMP, & special unit machines; Androids: peculiar machines: and amicable machines.
Providing you do the majority of the quests, the achievement should unlock through normal game play. The achievement is also available for purchase after your third playthrough at the special achievement shop. It costs 50,000 gold. If you plan on buying achievements at this shop, this would be a good achievement to buy. The 80% unit data mark is only attained by a fairly thorough exploration of the game. If you are unlocking achievements through game play, this achievement will come as a normal result of your game play. On the other hand, if you opt to limit your exploration and buy some achievements, it is quite likely that you will not attain the 80% mark and need to purchase this achievement as well.
Since more than 20% of the units do not appear until the third playthrough, this is the earliest the achievement can be unlocked. An efficient way to get the achievement is to play through the first two playthroughs thoroughly doing all or almost all of the available side quests. Almost all of the peculiar and amicable machine data is acquired through side quests. With the exception of EMP and enhanced machines, the majority of the rest of the unit data is acquired by playing through the story. During your third playthrough, in addition to unit data acquired in new side quests, EMP and enhanced machines often appear in place of normal machines in most of the game regions.
During your third playthrough, monitor your progress closely. Save frequently when your unit data hits the 78% mark. Check your unit data when you suspect you have encountered a new enemy type. You will get a notification that new unit data was acquired in the lower right hand corner of the screen. However, the notification is easy to miss and it is best to check the specific percentage frequently. The achievement will unlock as soon as your unit data reaches 80%. If it does not, you have, most likely, experienced a glitch.
In the event of a glitch, clear the cache. To do so, turn off the console by holding the
button on the console for at least ten seconds and then unplug the console for at least 20 seconds. Load the save you made just before reaching the 80% unit data mark. Clearing the cache will most likely remedy the problem. Return to the location where you reached 80% and repeat what you did previously. The achievement should now unlock.