In earlier days, the turntable was offered as No. 8998. It has been revised a bit with a new model number, No. 89980, with an improved controller and a transformer for roundhouse operation. The turntable motor has been improved over the earlier model. Additional tracks can be added to the table with item No 8997 (a package of eight).
Installation of the turntable requires that you cut a hole in your layout table. Because the turntable apron covers the cut edge, your saw work does not have to be absolutely perfect.
The turntable is more appropriate for steam locomotives, but diesels and sometimes electric locomotives were serviced in roundhouses. Likewise, the transfer table is more appropriate for electrics and diesels, but there were interesting exceptions to this rule also.