alexgoei Wrote:2002 part A Q2 Points Question.
I have tried indicating point-to-point on this table .
It is certainly a case for classic point-to-point; however I do wonder whether you'd be best off not attempting to show (as I think you are a little confused by it) but merely use that recognition as a prompt for getting the general locking correct.
If you do want to get the details of point-point correct, first consider the combinations
211N 212N valid
211N 212R invalid
211R 212N valid
211R 212R valid
Then think how one point can tell whether it can change from a valid to another valid combination.
Imagine yourself as 211.
Since the start position must be valid, if 211N then we definitely know 212 is N. Hence no restriction for 211N to R.
However if 211 starts R, then for it to go N it must check that 212N (since if 212R then an invalid combination would result); this is the point-point: 211 R to N requires 212N
Then imagine yourself as 212.
If 212N then it doesn't matter where 211 is; both combinations are valid.
However for it to go R then it must make sure that 211R (as 211N would give the invalid combination); hence there is point-point: 212 N to R requires 212R.
Note that the point to point locking affects each point just in the one direction and the two lockings are complementary. What we are saying is that "one or other or neither" may direct trains onto the diamond BUT NOT BOTH. The first one that does so prevents the other from so doing.
So you did get it right BUT then you went and spoilt it by finding erroneous stuff as well that rather detracted.