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Jim,
According to Eurocontrol's frequency list, you can not set 121.370. The proper ones around are 121.365 and 121.375. The 8.33kHz spacing just does not go to 121.370.
Here is the abbreviated list http://www.eurocontrol.int/sites/default/files/article/content/documents/communications/2016-03-frequency%20table.pdf
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