SAN JOSE — North America-based semiconductor equipment manufacturers posted $1.59 billion in orders worldwide in April on a three-month average basis, up 1.3% from April 2015 and up 15.6% from the revised March figures.

It was the highest mark in eight months for bookings, added the SEMI trade group, which releases the data.

The three-month average worldwide billings in April was $1.46 billion, down 4% from 2015 but up 21.5% from the final March 2016 level.

The book-to-bill ratio was 1.10, SEMI said. A book-to-bill of 1.10 means that $110 worth of orders were received for every $100 of product billed for the month.

The ratio is calculated by dividing the number of orders by the number of sales. A ratio above 1.0 is considered an indicator of an expanding market.