Unkown Platform Rocking Chair

I have been given this chair by someone who had it given to her by an elderly friend. I know it is a Platform Rocker, there my knowledge ends. There are no markings on it. The seat cushion has 4 springs underneath. The rocking mechanism (pictured) is one spring on each side. As shown, there are indications the right side spring once sat a little lower (an adjustment perhaps?). It appears that at some time someone re-upholstered it as the tacks on the rear are the kind of furniture thumbtacks sold today. The deep brown color is a stain over a much lighter wood visible where the chair bottom makes contact with the stop bar on the platform. There are visible no makers marks on it.