HP LaserJet P4010 and P4510 Series - Software Technical Reference
Page 176
...printing on the second side of the page, the printer makes adjustments to print on the second side of the media because the HP LaserJet P4014, P4014n, P4015n, P4015tn, P4515n and P4515tn printer models do not have a duplexing unit installed. Manually print on both sides Select the Print on Both Sides... adjustments for media types that is known as cardstock and thick media. Manually printing on the second side of a page is enabled in the driver, the printer automatically prints on both sides of media types that are supported for automatic duplexing (Letter, A4, Legal, and 8.5x13 only), ...
...printing on the second side of the page, the printer makes adjustments to print on the second side of the media because the HP LaserJet P4014, P4014n, P4015n, P4015tn, P4515n and P4515tn printer models do not have a duplexing unit installed. Manually print on both sides Select the Print on Both Sides... adjustments for media types that is known as cardstock and thick media. Manually printing on the second side of a page is enabled in the driver, the printer automatically prints on both sides of media types that are supported for automatic duplexing (Letter, A4, Legal, and 8.5x13 only), ...