Hi welcome to the forum.. You've come to the right place, someone will be along that knows stoker readings. In the meantime lets check the draft gauge. You have it mounted and leveled and is it calibrated to zero when its not hooked up to anything? Next, there is a high side port and low side port.. Take the reading with the low side port and leave the high side open. Keep in mind now that the negative value will be read on the positive side of the scale. This makes it possible to see values higher than -.05 since the negative side of the scale only goes that far.
Its critical that you have Carbon Monoxide alarms installed. If not, you should shut it down until you get at least two of them. By the looks of your readings, its possible you have positive pressure or close to it in the appliance cavity or flue pipe.. It's imperative that negative pressure is maintained in the entire system so that CO cannot leak out into the living space.
This much will get you started on diagnosis. Stay tuned as more will be along to help..