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Figure 1. Schematic diagram of the study design. Two Lunar Achilles+ ultrasound machines were assessed over different time periods. Six same-day trials (D1 and D2s) took place over the period of 1 year. Each trial day consisted of six consecutive measurements: three on Lunar1 (L1) and three on Lunar2 (L2). These within-day measurements took place at the beginning or end of a week, such that there were three week-long trials. The three testing weeks were scheduled at 6 month intervals yielding two 6-month examination periods. Finally, these two 6-month time periods constituted one 1-year test period. Subjects were scheduled for testing on as many D1s and D2s as possible throughout this 1-year testing period. n = number of measurements during each trial period. Trial days are shaded in grey.
