Should the DR1900 Rescan 100%T function in the system checks menu be set to "on"?
DR1900 Rescan 100%T function
When the Rescan 100%T is set to "on" the DR1900 will be forced to zero when a cuvette (TNT+ or LCK) program is selected. Generally the TNT+ or LCK vials do not need to take a zero, because the instrument will automatically use the air blank that was recorded when the DR1900 was manufactured. However, the optics can become dirty over time causing a shift on the zero value and inaccuracy in the measurement. The default is "off".