This covers the very basics of armory conflict in the Standards for Evaluation of Names and Armory (the new name for the Rules for Submissions).  If you need more details, see section A.5. of the Standards to see the exact rule.
Your armory must not accidentally be too close to any registered SCA armory or give the impression that you have a close relationship to a person with registered SCA armory, like being that person’s spouse or child. We call both of these things “conflict”.  
Your armory doesn’t conflict with someone else’s armory if it has a single large change from their armory or if it has two smaller changes like those used for cadency (medieval markers to show relationships in armory). In some cases, no matter how many technical differences there are, your armory may simply look too close to someone else’s – this is called “visual conflict”.  
Larger changes (sometimes called “substantial changes”) that make your armory not conflict with someone else’s (you only need one of these):
•	Your armory adds or removes the primary charge group.
•	Your armory makes a single substantial change that affects the entire primary charge group. This includes substantial changes in type, in number, in arrangement, or in posture of that group. Not all changes are substantial.  If you make a smaller change to the primary charge group, it may still count as a smaller change below.
•	Your armory makes a substantial change to the field, if it doesn’t have a primary charge group.
OR
Smaller changes (sometimes called “distinct changes”) that count towards making your armory not conflict with someone else’s (you need at least two of these): 
•	Your armory changes the field in a way that affects “half” the field. If your armory or theirs is a fieldless badge, it automatically gets this, even if both of them are fieldless.
•	Your armory adds or removes any charge group.
•	Your armory changes the tincture of at least “half” of any charge group.
•	Your armory changes the type of charges of at least “half” of any charge group.
•	Your armory changes the number of charges within any charge group. However, this doesn’t count if both groups have six or more (including “semy”) charges.
•	Your armory changes the arrangement of charges within a charge group or changes where the charge group is on the field (like “in canton”, or “in base”).
•	Your armory changes the posture or orientation of at least “half” of the charges in any charge group.
“Half” can be a little tricky - it’s easy to half two or four, but three or a group unevenly distributed around a line of division is more complicated.  Here are some rules on how to determine a not-numerically-half “half”:
•	When a group of three charges on the field is arranged two and one, the bottom charge is considered half the charge group.
•	When a tertiary charge group of three charges is on a central ordinary or chief, the centermost charge is considered half the charge group.
•	When the field is divided and a central charge or charge group is balanced around the center of the device, each side of the field is considered “half”, even if they aren’t evenly balanced.
•	When the field is divided or an ordinary splits the field into two parts and a primary or secondary charge group is split so that part of it lies on each side, each side is considered “half”, even if they aren’t evenly balanced.
No matter how many changes you make to the field or to a not-numerically-half “half” of a single charge group, you can only count them once.  For example, if you change the type and the tincture and the orientation of the middle of three charges on a fess, that only counts as one smaller change.
However, if you make multiple changes to a whole charge group or to a regular, numerically-half “half”, you can count all of those changes.
Changes that are smaller than a distinct change do not contribute to difference between two armorial designs, no matter how many of them there are, because these kinds of changes happened in period with artistic variation. That is, sometimes they were included and sometimes weren’t, or were sometimes depicted slightly differently in different drawings of the exact same armory.  This includes maintained charges and differences in artistic style, including details like having the tongue or claws a different color.  
Additionally, for certain charge types, all variants of that charge are considered equivalent for conflict purposes, and so don’t count as a substantial or distinct change.  For example, we consider all kinds of cats, from lions to wildcats to domestic cats, to be equivalent.  The same is true for swords and daggers, and for dogs and wolves and foxes, and for roses and cinquefoils.
If your armory does conflict with someone else’s registered armory, you’ll want to resolve that conflict before submitting, either by making changes or by obtaining written permission to conflict from them.  If you want to obtain permission and don’t know the person, talk to the heralds – they may be able to help track them down.