Units of measurement in the database
The problem is that you should not allow free-form values for the units, but have a second table of units and reference that with a foreign key:

CREATE TABLE unit (
   unit_id bigint PRIMARY KEY,
   name text NOT NULL
);

CREATE TABLE measurement (
   measurement_id bigint PRIMARY KEY,
   unit_id bigint NOT NULL REFERENCES unit,
   value double precision NOT NULL
);


That guarantees that you can only store existing units in your measurement table, which is good for data quality (and it is not much extra effort).

Otherwise you can end up with entries like cm, centimeter, centimeters and Zentimeter all meaning the same thing.