The IBM Adjustable Keyboard and Lexmark Select-Ease Keyboard were tenkeyless ergonomic keyboards based on the Model M1/M2 design, possibly being the last IBM-sanctioned Model M design. As such, they were the final form of the Model M in its classic era, being the unique last model introduced before Lexmark stopped Model M production. Being the only ergonomic keyboard as per today's standards that IBM ever marketed, the Model M15 features a high degree of customisability, including split, tilt, swivel and tenting capabilities. For convenience, the arrow keys are duplicated on both halves of the keyboard and the split spacebar has the Erase-Eaze feature. Model M15s are quite rare and sell handsome at auction, with many considering these to be the holy grail of the Model Ms.