VeteranRatio
This flag determines how many times the own value in credits a unit must destroy in order to be promoted. It is based on the Cost= values of objects and a straight multiplier. Note that this isn't limited to enemy objects. Civilian/Neutral as well as your very own objects count, too.
Example
The default setting for VeteranRatio is 3.0, the default price for a GI is 200 and the default price for a Conscript is 100. Therefore, in order to gain veterancy, a GI would have to destroy objects worth 200 * 3.0 == 600 credits for a promotion of one level. That could be, for example, six Conscripts, one Robot tank, or two Flak Troopers. The Conscript, however, only has to destroy 100 * 3.0 == 300 credits worth of shit to get promoted, meaning two GIs would be enough.
As you'll surely recognize, this means two things:
- Destroying an expensive object with a cheap unit results in a very high chance of instant or very soon promotion
- Expensive units need to destroy a lot of stuff to get promoted (1 Prism Tank --> $1200 * 3.0 == $3600 == 36 Conscripts)
Exceptions
Objects flagged as DontScore=yes or Insignificant=yes do not count as kills, and therefore don't add to the total amount of credits destroyed by a unit. As such, they don't bring them closer to promotion, either.