A Short Instruction On Fasting & Abstinence (including the difference between modern and traditional fasting rules): The Missionaries of St. John the Baptist, an order of Latin Mass priests in Kentucky, published a good guide on fasting and abstinence during Lent: https://mcusercontent.com/61eba0fda529907fc1dacf176/files/ee1ae3df-d987-4f22-920f-7d5deaebced0/Rules_for_Fasting.pdf