Abstract: A centerline marker holder used for engaging and sliding along a portion of two intersecting walls and sliding along an exterior or interior rounded or bull nose corner between the walls. The marker holder uses a pencil for drawing a centerline along a length of the corner. The marker holder includes a flat, first wall engaging member attached at an angle to a flat, second wall engaging member. Along a length of an intersection of the first and second wall engaging members is a centerline hole. The centerline hole is dimensioned to receive the pencil therethrough for marking the centerline. The marker holder also includes a plurality of offset holes from the centerline hole for drawing parallel offset lines at a selected distance from the centerline.