It is interesting to note that different MOND theories offer (very) different answers to the generic question “acceleration with respect to what?”. For instance, in the MOND-from-vacuum idea (see [304Jump To The Next Citation Point] and Section 7.10), the total acceleration is measured with respect to the quantum vacuum, which is well defined. In BIMOND (Section 7.8) it is the relative acceleration between the two metrics, which is also well defined through the difference of Christoffel symbols.