Lettuce is a hardy crop that can be started throughout the growing season. It prefers cool temperatures, growing best at 16°C to 19&degC. Approximately 900 seeds / gram.
Hints:

Plant 7 mm [1/4"] deep in rows 30 to 60 cm [12-24"] apart.

Thin to 20 cm [8"] rows.

Plant 2 to 3 times deeper in the fall for the earliest spring lettuce.

Buttercrunch - 66 days. Long standing, slow bolting variety. The dark green butter heads are very compact and crisp. Considerable heat resistance. Fine for home and market gardens.