Old Analytical Balance
Fine adjustment to the balance is via the sliding weight on the scale arm seen here. That's done via a mechanical linkage operated by the knob on the right side of the case. The knob at the bottom center is the lock for the balance beam. The lock is engaged at all times, except when actually reading the mass or estimating the needed adjustments when "zeroing-in" on the final mass reading.
Old Analytical Balance
Fine adjustment to the balance is via the sliding weight on the scale arm seen here. That's done via a mechanical linkage operated by the knob on the right side of the case. The knob at the bottom center is the lock for the balance beam. The lock is engaged at all times, except when actually reading the mass or estimating the needed adjustments when "zeroing-in" on the final mass reading.