code: func (f *Field) setTimeQuantum(q TimeQuantum) error {
  	f.mu.Lock()
  	defer f.mu.Unlock()
  
  	// Validate input.
  	if !q.Valid() {
  		return ErrInvalidTimeQuantum
  	}
  
  	// Update value on field.
  	f.options.TimeQuantum = q
  
  	// Persist meta data to disk.
  	if err := f.saveMeta(); err != nil {
  		return errors.Wrap(err, "saving meta")
  	}
  
  	return nil
  }
docs: // setTimeQuantum sets the time quantum for the field.