I am going to try for 'many topics one post' with this post...
There are some great comments to one of my previous posts, and it is easier to comment and expand on them here instead of in the Comments section. It does require me to explain the Impetus rules a bit more closely.
Units have 7 basic characteristics: class, base size, move rating, VBU, Impetus, point value, and any special notes.
CLASS: There are several classes for the troops - heavy infantry (FP), light infantry (FL), missile troops (T), skirmishers (S), artillery (ART), elephants (EL, but will represent Serudla, Sro, etc), and a variety of mounted troops which I am not going to worry about until I start up the historical counterpart.
(the abbreviations might not seem appropriate, but are taken directly from the Impetus rules and are a holdover from the original version of the rules which are written in Italian)
BASE SIZE: The size of the base for each individual unit is typically based on the Class of the troops. In Impetus, the base width is most important. 120mm is the standard base width when using 25/28mm miniatures. The base depth varies per class: heavy infantry use a 40mm depth; light infantry and missile units use 60mm; skirmishers use 30mm. Artillery and large creatures can have a base depth that fits with the minis being used; this can be 80mm or more if necessary. I like the different base sizes for the different troops, as it is a subtle mnemonic device to remind players of their troop's capabilities.
MOVE RATING: This is how far a unit can move on the tabletop each turn. This is often related to the unit's class. In the historical unit ratings, a unit of heavy infantry typically has a move of 5U (U is a generic Unit of measure which is different for the minis used, i.e. 1U = 1cm for 15mm minis, 1U = 2cm for 25/28mm minis). Light infantry and skirmishers typically have a Move of 8U. Thus, a unit's CLASS, BASE SIZE, and MOVE are all interconnected.
VBU: Ah, now for the good stuff. VBU is a unit's Basic Combat Value. This is the number of D6 dice that a unit has for melee and/or missile combat. This can be increased due to charging or reduced due to losses, among other things. When looking through the unit stats for the historical armies on the Impetus site, the highest VBU for foot troops is 6 (16th century samurai). I intend to use this as the 'top end' of the scale for human troops on Tékumel, so the first cohort of the First Legion of Ever Present Glory will have a VBU of 6.
IMPETUS: Another important number. The Impetus rating of a unit is the number of bonus D6 that can be thrown when a unit charges. This number ranges from 0 to 4 for foot troops. If a unit has an Impetus rating of 0, it can not charge. Skirmishers and most missile and light troops have an Impetus of 0. There are, of course, exceptions and this number, along with the VBU, will be one of the more 'interesting' parts of my project as I come up with combat values for all of my troops.
POINT VALUE: Listed as VD (Demoralisation Value) in the Impetus rules, each unit has a value or cost in the army. This can range from 1 to 3. When a unit is routed (destroyed), the Point Value is subtracted from the army total, and when the army loses 50% of its points, the army is routed and the game has ended.
SPECIAL NOTES: This can be as simple as listing the missile weapon used - slings, javelins, long bows, etc. to noting any special detail a unit might have. Some troops are Impetuous - they must pursue a retreating enemy unit. Others might have special movement allowances. It is just a small patch of chrome to help differentiate special units.
There are several points that I will need to re-align for the conversion of the historical Impetus rules into the Tékumeli Impetus version. The most obvious is the VBU + Impetus values for the individual legions. This is where my friends Kagesh and Chirine make some very useful insights. The missile-equipped cohorts of the heavy infantry legions should be quite capable of melee combat, if not so well-equipped as their specialized counterparts in the legion. By giving these cohorts an Impetus score, it makes them much more useful for combat and it gives the player a choice - melee or missile fire (you can not do both in Impetus). I do not think that a specialized missile unit, say the Legion of the Clan of the Broken Bough, should have an Impetus score, therefore they are unable to charge the enemy (a unit without an Impetus score can defend itself if charged, however).
In relation to this, I am thinking that there needs to be an addition to a unit's characteristics. A Missile score, I think, will be very useful to help differentiate between special missile units - like the Broken Bough troops - and the bow-armed heavy infantry troops. A cohort of Broken Bough troops should be able to outshoot the Ever Present Glory cohorts in my opinion, but as Impetus is written, they could not unless the Broken Bough unit has a large VBU, which would then make the lightly-armored and armed missile troops very good in melee. Hmmm, more calculations!
I am also not a big fan of unit point values. I might not use this at all, or I might alter the army's break point value from 50%. A scenario could change that to, say, 40% for troops or leaders that are not that interested in fighting or are exhausted. The army break point could go up - 60% or more if the army is suitably desperate.
I'm also starting to rethink the base sizes. Maybe the bow-armed cohorts of a heavy infantry legion should be on the heavy infantry bases (120mm x 40mm) instead of the light infantry/missile bases (120mm x 60mm). All of the cohorts of the heavy infantry legion should have the same move rating, yes? ... hmmmmmm
Wow, lots of words there - I hope you made it through without a headache!