Those things are of limited use in bow making.
That reading is simply for the surface wood, which may well be 10%. What matters from a bow making point of view is how dry the stave is in the middle
The simplest way to check your staves moisture loss is to weigh them. As the water leaves they become lighter
Keep a check on the weight until it stabalises for at least a few days. Then rough out the bow and repeat the process.
After a while you can do it by feel alone.
Another thing you can do is to remove a piece of wood and weigh it. Then oven dry it until at 0% mc and again weigh it. Then work out the %age of m.c.