Why does the P come before the Q in relative displacement vector notation?

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Ultrimo
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We have 3 points. O, P, Q.

OP = rP
OQ = rQ
but why is QP PrQ rather than QrP?

I'm just starting M4 and I really like to understand everything. This doesn't make any sense to me and I can't find out online. I'm sure there's a logical reason for it to be like that. Is it because you go along to rQ and then along to P?
 
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Ultrimo said:
We have 3 points. O, P, Q.

OP = rP
OQ = rQ
but why is QP PrQ rather than QrP?
Your notation doesn't make any sense to me.

QP = OP - OQ

If the coordinate form of OP is <p1, p2>, and the coordinate form of OQ is <q1, q2>, then QP = <p1 - q1, p2 - q2>.
Ultrimo said:
I'm just starting M4 and I really like to understand everything. This doesn't make any sense to me and I can't find out online. I'm sure there's a logical reason for it to be like that. Is it because you go along to rQ and then along to P?