This is my favorite useful mechanical pencil for a number of reasons: 1) Relatively Light Weight. I find this good for avoiding fatigue; 2) Wide, Triangular Grip. Again, I find this more comfortable than a narrow mechanical pencil. However, one would not want to use this pencil for drafting purposes and using a ruler or guides (because of the relative girth). Please note that the rubberized material in the grip can become twisted over years of use and become slightly loose at the edges; 3) Durable Lead Advancing Mechanism. I never had one fail after years of use. Usually, someone walks off with the pencil before it ever has a chance to break!; 4) A Usable Eraser (Big, Polymer, No Cap, Retractible, Long). Inadequate erasers are my biggest complaint with mechanical pencils. If a person erases as much as I do, you will be frustrated by pencils that require the frequent removal of either a tiny or large cap end to access the eraser (doing so wears out those pencils, and the caps can be easily lost). Furthermore, most erasers are abrasive and tiny: They rip the paper and need to frequently be refilled. The PhD and PhD Ultra pencils have a wide, polymer twist eraser that conveniently can be retracted. It is also generous in length and can inexpensively be replaced by cutting a Pentel Click Eraser refill to the appropriate length!; 5) Price/Value Ratio. I've tried dozens of less-expensive and more expensive pencils and find that the PhD and PhD Ultra provide a high level of performance for a reasonable price. The regular PhD model can be found for around $**** at ******, but is difficult to find elsewhere. It is possible that the PhD Ultra model is now discontinued (it is no longer found on the Papermate Web site or in brick-and-mortar stores).