SENA devotes over 10,000 words to conflict checking armory, which the below guide attempts to summarize.
It includes references to the relevant sections of SENA so you can track down more details if needed.
To conflict-check a new piece of armory, search the armorial database to find a list of all existing registrations which could possibly conflict, then review the new item against each of them in turn.
Work through the list below until you find that they are clear of conflict through at least one Substantial Change (SC) or two Distinct Changes (DCs).
If you reach the end of the list without finding an SC or two DCs, the items conflict and the new one can not be registered without permission to conflict. (A5H)
First, identify the charge groups in each piece of armory. (A3D)
If one piece of armory has a primary charge and the other doesn’t, that’s an SC. (A5E1)
If there is a primary charge group, any of the following changes to it is an SC:
- Type of all charges are substantially different? (A5E2)
- Number of charges is substantially different (1, 2, 3, more than 3)? (A5E3)
- Arrangement of charges is substantially different? (A5E4)
- Posture or orientation of charges is substantially different? (A5E5)
If there is no primary charge group, any of the following changes to the field is an SC:
- One field is divided and the other is undivided? (A5F1a)
- Direction of lines of division has changed? (Number of lines doesn’t count.) (A5F1b)
- No tinctures in common? Or for divisions into two, three, or four pieces, each section has changed and each item has at least one tincture the other does not? (A5F2)
For the field, each of the following is a DC — however, if there is a primary charge group, you can only get one DC for the field regardless of how many changes there are:
- Is either item (or both) fieldless? (A5G1e)
- Tincture changed for at least half of the field? (But if divided into more than four parts, swapping or rotating tinctures does not grant a DC.) (A5G1a)
- Direction of line of division has changed? (A5G1b)
- Style of partition line has changed? (A5G1c)
- Number of pieces is different (1, 2, 3, 4, more than 4)? (A5G1d)
For each of the charge groups, each of the following is a DC:
- Entire charge group has been added or removed? (A5G2)
- Type of charge changed for at least half of the group? (A5G4)
- Tincture changed for at least half of the group? (A5G3a)
- Addition of division line, or change in direction, style, or number of pieces (1, 2, 3, 4, more than 4)? (A5G3b, A5G3c, A5G3d)
- Number of charges is different (1, 2, 3, 4, 5, more than 5)? (A5G5)
- Arrangement of charges in the group is different (and it wasn’t forced by contrast rules)? (A5G6)
- Posture or orientation of the charges is different? (A5G7)
See also: A more-detailed guide that includes visual examples of each of these types of checks is found in Master Modar’s 2015 conflict-checking guide on Calontir’s heraldry site.