The Medway Handyman wrote:

What I can't work out is the 1-7 scales. In each case the 1 egg mark is
higher up than the 7 egg scale, so it indicates that 1 egg requires more
water to cook than 7 eggs would?

The more eggs you're cooking, the more volume within the cooker is taken
up by eggs, so the less volume of steam you require to fill the remainder?