Early microscope slides were typically made of wood or ivory with round recesses to hold samples and glass mounts. Glass tubes were also used as slides. The modern glass slide became the norm by the early to mid-1800s. Reference slides for biology, geology and medicine were produced from the late 1800s and often come in a wooden box with stacked trays of over 50 to 100 slides. Microscope accessories include eyepieces, objectives, micrometer eyepieces, adjustable stage micrometers, substage condensers, substage pollarizers, bulls eye lenses, condensers, interference plates, filters, tweezers, probes, sample pins and clamps, live boxes, fish troughs, heating and temperature stages, polarizing eyepieces, drawing eyepieces, camera lucida eyepieces, paraffin microscope lamps, incandescent gas lamps and arc lamps to mention the most common. Eyepiece micrometers are eyepiece lenses inscribed with a graduated line (graticules) in micrometers. Stage micrometers are mechanical stage devises that come from the manufacturer either permanently integrated into the stage or as an accessory attachment. They are used to orient microscope slides by x and y horizontal coordinates. Precision micromanipulators with tiny scalpels, needles, wrenches and other mini-tools, invented in 1859, can manage maneuvers down to 5-micrometer increments. The Berek compensator is a variable wave plate micrometer that slides into a slot above the objective in petrographic microscopes to determine the retardation position of interference colors for mineral identification. Vertical illuminators like the Berek illuminator screw onto the nose of petrographic microscopes for reflected light microscopy. It has an objectives clamp at the bottom. The Wright eyepiece is a polarizing accessory with a 360 degree adjustable dial and a slot near the bottom for wave plates.