Forgive me if the answer is obvious or can easily be found (I really looked and tried to figure it out, but - maybe because I'm not a native English speaker - it's still not clear to me).
Armor encumbers a character. Each piece as an encumbrance value. Let's take scale armor as an example, each piece has 3 ENC. For a full set (seven pieces), you add that together, resulting in 21.
The rules now state that to get the initiative penalty, you divide that by 5 and round up, resulting in an initiative penalty of (-)5. The example on the same page in the rulebook seems to indicate that my understanding is correct as the initiative penalty for half plate is exactly calculated this way in the example (resulting in -6).
Later on, the rules say that for WORN armor, only half of the armor's encumbrance is counted towards encumbrance. My understanding is, that it is only referring to the calculation of how much a character is carrying and if he is or is not burdened/overloaded.
But: the Mythras excel character generator that can be found (even on Design Mechanism's homepage), uses that "half of the armor's encumbrance" rule also when calculation initiative penalty. It says "armor encumbrance when worn 11" (not 21, so it halves armor encumbrance) and then says "armor penalty to strike rank -3 (not -5). And under "initiative" for that character it says "13" (the characters initiative without any armor is 16, so there is indeed only a -3 penalty applied).
I also encountered the same calculation with some pre-generated characters I found on the net.
What's your interpretation?
The question has more consequences:
In Fantasy Classic, armor wearing arcane spell casters
"must increase the Casting Time by 1 per 3 points of Initiative Penalty imposed by any armour worn. For example, the Initiative Penalty for a full suit of Scale armour is 5. A mage attempting to cast spells while wearing full Scale armour would add 2 to whatever the casting time of the desired spell was (Initiative Penalty of 5 divided by 3 equals 1.66, rounded up to 2). Therefore, if the caster was attempting Magic Missile, a spell with a casting Time of 1 Action, the casting would not be complete until he has used 3 consecutive Cast Actions (1+2=3)."
That again supports my interpretation. On the other hand, I find the armor encumbrance rules as I interpret them to be quite severe. So is the excel generator simply a bit buggy in that case? Do other player/GMs have house rules that apply the less severe rules?
And: what about the Classic Fantasy Fighters armor proficiency that says: " when worn, only 1/4 the total ENC of the armour is counted towards Encumbrance instead of half."
Sorry for the long post ... any light you can shed on this confusion of mine is very welcome (and I hope I could express my points adequately, remember, English is not my native language).