Set the letter's value in the Refers To box. You can create a value from data in a cell in the worksheet or you can add your own number. By default, Excel puts a reference to the currently selected cell in the box. If this contains your value, keep the default.
Gravely (the adverb) comes from the adjective, which comes from Latin (gravis), where it meant heavy or serious (this is where we get gravity--heaviness). Gravely ill means seriously ill, not soon to be in the grave. (and proof [1]). Bonus tidbit: grave (the noun) comes from words that originally meant to dig then a place dug, as for burial or, a grave. This is the same root as engrave.
While using different specific language, most states provide that people can be involuntarily committed to a mental institution if the person is: Mentally ill, and Danger to self or others. In many states, the dangerousness is supposed to be fairly immediate or imminent. Also, many states provide that even if the person is not dangerous, he/she can be committed if he/she is unable to take care of him/herself. In many states this is called being gravely disabled. The United States Supreme Court case of Foucha v.