If you are one of those people who is perfectly happy with the zone implementation in MC3, then you may not need to read further. But if, like me and my group, you aren't entirely satisfied with some of the implications of the zone-based combat system, read further!
Every combat encounter (or any encounter where distance and time may matter) can be assigned one of three Combat Scales: Close, Medium, or Long.
In Close Scale, a zone is approximately a 10 meter (or yard) cube. A combat round is about 5-10 seconds.
In Medium Scale, a zone is approximately a 50 meter (or yard) cube. A combat round is about 30-60 seconds.
In Long Scale, a zone is approximately a 100 meter (or yard) cube. A combat round is about 1-2 minutes.
Implications of Scale
If using Combat Scales, you can use every rule in the MC3 books almost as written. There are two major differences, however: (1) Weapon/Attack ranges and (2) Bonus Actions.
For purposes of weapon, ability, communication and Observation tests, ranges are measured as follows.
In Close Scale, everything within your zone and 5 additional zones is in Close range. Beyond that is Medium range. There should not be Long range in a Close Scale combat. Close Scale should be used for the interiors of most human-built buildings, sewers, large vehicles, and very often works well for fights within big cities, like Luna or San Dorado.
In Medium Scale, everything within your zone is in Close range. Everything between your zone and 5 zones away is Medium range. Beyond 5 zones is Long range. This is an appropriate scale for fights in the streets, in Venusian jungles, or inside cavernous citadels or Mercury's caves. If you choose not to move at all in a round using Medium Scale, you gain a bonus Restricted Action, which can be combined with your other Restricted to make a second Standard Action.
In Long Scale, everything within your zone is in Medium range. Everything up to 5 zones away is in Long range. Beyond 5 zones is Extreme range. This Scale works well for battlefields, air-based chase or combat scenes, or running skirmishes in wide open spaces (like Mars deserts). If you choose not to move at all in a round using Long Scale, you gain a bonus Standard Action.
Movement using Scale
The beauty of this system is that you use the movement rules exactly as written. The Combat Scale adjusts the time and distance to create believeable movement speeds. Because movement is largely what uses time in this system, if you choose not to move, you gain bonus actions as described above.