This is what I came across today (it's my app giving me an overview of what it's doing):
[3] => Extension: ext_hull_upgrades (level 3) applies Hungarian Math™ [ 1025 * (1 + (5 / 100) * 3) ], or 15%, to item def_arbalest_bot's armor_max, going from 1025 to 1178.75
[4] => Extension: ext_mechanic (level 4) applies Hungarian Math™ [ 1178.75 * (1 + (2 / 100) * 4) ], or 8%, to item def_arbalest_bot's armor_max, going from 1178.75 to 1273.05
[5] => Modifier: added -28 % (from def_standard_mass_reductor) to robot's armor_max, going from 1273.05 to 916.596
So, that's rounded, between 917 and 916. Even if I round (or floor) the answers in between, I can't get it below 915. The problem? In-game runtime value (blue on show info) is 914 HP.
I'm like, GRRR.
Mechanics is at 4, complex mechanics at 3, for an Arbalest. Also includes a T1 standard lightweight frame, using a standard (1 - 0.28) calculation.
edit: found it.. you can't stack calculations, it needs to go in one go; e.g. base * (1 + (4*0.02 + 3*0.05)). Nice.
Okay, here we go:
[3] => Extension: ext_hull_upgrades (level 3) applies Hungarian Math™ [ 1025 * (1 + (5 / 100) * 3) ], or 15%, to item def_arbalest_bot's armor_max, adding 153.75 (armor_max is now 1178.75)
[4] => Extension: ext_mechanic (level 4) applies Hungarian Math™ [ 1025 * (1 + (2 / 100) * 4) ], or 8%, to item def_arbalest_bot's armor_max, adding 82 (armor_max is now 1260.75)
[5] => Modifier: added -28 % (from def_standard_mass_reductor) to robot's armor_max, going from 1260.75 to 907.74
Smooth sailing? Nope, 907 HP??!! I know without demob it's 1261 (yup, a rounded up display value), so I'm guessing it's more than likely the reported 28% HP reduction from a demob is in actually more like 27.5%? Damn guys.