While there are plenty of books on figure drawing and fine art in bookstores, precious few appear on the art of design sketching. Learning Curves is Klara Sjolen's follow up to her 2005 book Design Sketching. Students at the Umea Institute of Design generated the content of the earlier book, while the more recent book showcases the output of working designers.
While Curves could be characterized as a sequel of sorts to the first book, drawing is a deep enough field that either book could be used as a starting point. Learning Curves is thicker and includes a broader range of modern techniques (e.g. using 3D CAD models as sketching templates, marker and Photoshop). Both books include demos on ellipses, shadows, perspective and materials. The 2005 book has more detailed tutorials on form and the more recent has one of the finest descriptions of different pens or materials we've seen yet. It is also testament that the earlier Sketching showcased extremely capable work from the students at Umea, since even a professional would be hard-pressed to determine whether a given sketch from either of the books was generated by a student or a pro.
The major difference between the two is the approach. While Design Sketching focuses on a series of tutorials defined by the product being drawn and the techniques required to generate the forms, Learning Curves presents nearly finished product sketches with "tips" from the experts on how to get the most out of technique. Either book does a nice job of providing a framework for learning how to sketch objects, but there's a lot more breadth in the more recent book, as well as a cleaner design aesthetic.
Since Design Sketching, Sjolen has moved from a teaching role to a postion at Scandia Trucks and Curves includes more Transportation design (with an emphasis on trucks) than her prior effort. The range of output is broader as well, with some sketches approaching childlike simplicity and others that seem as tight as a drum. Anne Forschner's car studies of classic vehicles approach photorealism in the beginning, though her later work gets so loose that it barely describes the vehicles she's conveying. Likewise, Mark Juhasz's work ranges from nearly naïve photoshop renderings of foxes to color studies of a mundane chocolate bar that would make Gerhard Richter jealous.
Design Sketching treats product drawing as a Platonic ideal of illustration. The examples in that book convey sketching in the "cleanest" way possible, giving as many hints about form and shape as possible with the fewest lines. It represents industrial design as illustration and avoids ambiguity on all levels. Learning Curves however, takes a different approach, and shows creative using drawing as a form of expression. Much like the difference between a 5 minute sketch in figure drawing and an hour, the curves in the 5 minute sketches need to convey the essence of a thing, or a gesture in drawing parlance. Both approaches need to be part of any designer's toolbox. While Sketching is likely a more definitive starting point as a manual of style, Learning Curves is probably a bit more fun. Educators everywhere will tell prospective students not to be "precious" with their work and that hint is mentioned again on page 56. Unfortunately while the diversity of techniques displayed in Curves is probably a good way to expand the range of any potential designer, employers still seem to want design sketching to obey a certain set of rules that obey a very particular aesthetic and in order to make those stylistic compromises while retaining the loose quality that's always mentioned but can't exactly be taught, the only way to get there is practice. Either book is a nice place to start.