A powder container includes a body and a pair of walls that block one end of the body and the other end. The timing adjustment circuit at least consists of a second timing adjustment unit, a multistage sample circuit, and a decision circuit for adjusting received timing of an output signal transmitted by a first chip and received by a second chip. One or more optical beam splitters divert the assistant’s beam path to the assistant’s tube via the back of the housing of the stereomicroscope. In this manner, data may be extracted from the data stream despite a varying or unknown phase or duty cycle, or in the presence of jitter. These instruments include a spacer trial or set of spacer trials for determining the appropriate size spacer required for a particular surgical procedure, a spacer introducer for grasping and positioning a spacer at least partially within a receiving bed formed in the intervertebral space, and a bone tamp for driving a spacer into the receiving bed.