Small, pocket sharpeners are ultra-lightweight and can fit anywhere. Some expensive models, made of aluminum or brass, even have replaceable blades. Problem is, there is no receptacle for shavings, which can be messy unless you can sharpen over a trash can. Bullet sharpeners, however, have a built-in receptacle, so you never need to worry about shavings flying everywhere in the middle of an exam. They are bigger, but only slightly so and they still weigh almost nothing, so they are easy to stash in an outer backpack pocket or purse.