What is the unit of the field prism.did.signal?

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According to epan/dissectors/packet-ieee80211-prism.c the value is dBm.

 119  * I infer from the current NetBSD "wi" driver that "signal" and "noise"
 120  * are adjusted dBm values, with the dBm value having 100 added to it
 121  * for the Prism II cards (although the NetBSD code has an XXX comment
 122  * for the #define for WI_PRISM_DBM_OFFSET) and 149 (with no XXX comment)
 123  * for the Orinoco cards.