Because default lenght for char type in this case is one caracter, IOW it's the same as

declare @sOsmOsc char(1)

I recomend that you always specify size.

declare @sOsmOsc char(3) 
-- Or
declare @sOsmOsc varchar(32)

>I thought this was as simple as it gets but:
>Can someone tell me why the following IF statement fails?
>I would have expected this to match but my SET command only executes if I set the condition to !=.

>Declare @oscString character
>declare @sOsmOsc character
>set @sOsmOsc = 'OSC'
>
>IF @sOsmOsc = 'OSC'
>       SET @oscString = 'T'