The present application is directed to a method for determining photolithography focus errors during production of a device. The method comprises providing a substrate and forming a photoresist pattern on the substrate. The photoresist pattern comprises a device pattern and one or more blocking scheme patterns. The process further comprises performing a device manufacturing process using the photoresist pattern as a mask to form sensor windows on the substrate. One or more focus error sensors are formed in the sensor windows. Focus errors are determined using the focus error sensors. Other embodiments of the present application are directed to wafers comprising one or more focus error sensors positioned in sensor windows.