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This program monitors the sensitivity of three NUV gratings to detect any changes due to contamination or other causes. Observations execute twice a year (in approximately February and August). Beginning in Cycle 24 comma additional cenwaves were added for the medium-resolution gratings (G185M-2010 comma G285M-2850 comma G225M-2306 comma and G225M-2410). Beginning in Cycle 26 comma monitoring of G285M was discontinued due to its low sensitivity and lack of usage over the past few HST cycles. Given these considerations comma the user community is urged to use STIS instead. If for any reason there is a need to use COS-G285M comma the monitoring of this mode will be reinstated.