Lyre harps: string count and what it changes
Seven, sixteen or nineteen strings — what each range allows, how tuning works, and why a lyre is one of the easiest instruments to start.
Violin sizes, and how to measure for one
What 4/4, 3/4 and 1/2 actually mean, how to measure an arm properly, and why a too-large instrument is worse than a too-small one.