An image forming apparatus, such as a printer, may have a horizontally-loaded drawer containing, for example, a toner cartridge or an image forming unit having toner. An estimate of the conditional probability distribution is compared for the signal state based on the state data for particles under consideration and such particles are resampled upon receipt of sensor measurement data. The upper segments in a first row are offset 180 degrees from those in an adjoining row to provide greater coupling of magnetic flux. The pressing plate defines an avoiding hole. In yet another form, at least certain of the machine tools are movable parallel to the work-holding conveyor so that they may be predeterminately moved prior to andor during operations on work. The seat member may be removably installed in an operative position on the upper side of the first platform through a releasable engagement of the first and second male-female engagement members with one another.