Heybrook HB1 Renovation

[gbcambridge]

I recently acquired a pair of these fine old speakers, Heybrook HB1. (Mine are serial number 011053). The cone surrounds were shot (not unusual) but all else appeared to be OK. However, I wanted to review the crossover and there came the problem.
It appeared difficult to obtain a diagram of the crossover. I finally found one and everything agreed with my actual crossover except that my actual resistor is rated at 15 Ohms, while the published circuit states 18 Ohms. I say "published" ...it is actually a freehand sketch by someone.

So, can anyone advise on this? I am hesitant to change what was implemented but I am curious as to the actual reason the resistor disagrees with the diagram. I have since found a diagram for a Series 2 crossover and there they are also showing an 18 Ohm resistor!