Flexible chuck with strain gauge

A method comprising:

• applying air pressure to an air cavity enclosed in part by a flexible portion of an annular flexible chuck and a superstrate of a shaping system, wherein the annular flexible chuck holds the superstrate, and wherein applying the air pressure to the air cavity causes the flexible portion and the superstrate to bow;
• obtaining strain information about the flexible portion of the annular flexible chuck;
• and
• adjusting the shaping system based on the strain information.

A shaping system comprising:

• an annular flexible chuck adapted to hold a superstrate;
• a pressure controller adapted to increase or decrease an air pressure in an air cavity enclosed in part by a flexible portion of the annular flexible chuck, wherein increasing or decreasing the air pressure while the annular flexible chuck holds the superstrate causes the flexible portion and the superstrate to bow;
• strain gauges that are configured to measure strain at different locations on the flexible portion of the annular flexible chuck and to generate strain measurements that indicate the measured strain;
• and
• a controller configured to estimate one or more shape-characteristic values of the annular flexible chuck based on the strain measurements received from the strain gauges and adjust the shaping system based on the one or more shape-characteristic values.