One of the items Tiny can collect is Nanometal. Nanometal was use to create the SenTrax army, and as such, Tiny can recycle it (See: Underground Recycling Center) for his own use. The lower bar in the upper-left corner of the HUD represents the amount of Nanometal currently stored by Tiny. Nanometal is important because it allows Tiny to regenerate his Fix-It Crabs, Teeny Weeny Tanks and his Hitpoints. Tinys internal systems constantly monitor his condition and will repair any damage or rebuild other resources by using a portion of his stored Nanometal. Without Nanometal, Tiny can't regenerate any of his systems.
Nanometal is a pun for Nanometer which is a a is a unit of length in the metric system.