Example: 52s90cb: examine the picture:
1. The rule is to follow a single, unbranching chain starting at the candidate labelled A, through all the candidates
labelled with capital letters B,C etc up to the last capital (here E) and then to continue via labels a, b, c etc to the end, (here v). We may proceed only to placeable candidates, whether Red or Blue conditionals, or unconditional True (marked with Black). As we reach each new label, we must also mark all those candidates it deletes, whether conditionally or unconditionally, in the appropriate colour.
2. Starting at the A: this labels the conjugate Red254: the marking of the set of conjugates, with their deletions, is done prior to the derivations discussed here.
3. From A, follow the green line to candidate B, the Red272. It's in a red rectangle - horizontal, meaning it's the last red 2 in the row. Check r7 to verify this: the only other 2 in the row is slashed vertically, so we look from it vertically to see what has caused the slash. We see the candidate A. This assures us that the conditions for B were already in existence before we got to B, as A precedes B.
4. Follow from B to C. There is no candidate placed at C: strictly, we should have omitted C and continued our labelling at r9c6. So let's look at D. D labels 296 with a red circle, meaning a red conjugate. By this time,292 has been cut (slashed) by both red and blue cuts, which is an unconditional deletion, so that D is truly a red conjugate.
5. Follow to E, where 2 is labelled as blue conjugate. The green line ends here, and recommences at (a).
6. (a) states that 927 is a blue conditional, the square shows that it is the last candidate in the cell - the 1 has already been cut in r2 (due to the conjugate at r2c1).
7. (b) and (c) are straightforward. The green rectangle at (d) is an error, please just ignore it. We see the blue 8 in a horizontal rectangle, meaning it's the only blue 8 left in the row - and yes, we see that 859 was cut by the original blue conjugate 259.
8. And that's all there is to it - you can visit any cell, that contains a labelled candidate, and see immediately why that candidate has been placed.
9. It is not essential to mark all cuts caused by a placement - you can leave out those you will not need to rely on in future placements. So, for instance, I have not cut the 1 or 7 in r5c9.
10. The example ends at (v) as two blue 8s have appeared in box 8, confirming all reds as true, which leaves us with a puzzle rated SER 7.3. That will require another diagram.