Implemented negative values on si tagdisplay

    def type_bit(self, value):

        '''Bit type'''

        if value.isdecimal():

            v = float(value)

        if value.startswith('-'):

            value_without_minus = value[1:]

            neg = True

        else:

            value_without_minus = value

            neg = False

        if value_without_minus.isdecimal():

            v = float(value_without_minus)

            if v >= 1000:

                si = "KMGTPEZY"

                p = min(math.floor(math.log(abs(v), 2)/10.0), pow(2, len(si)))

                d = v / pow(2, 10*p)

                u = si[int(p-1)]

                value =  u"%.4g%si"%(d, u)

                if neg:

                    value =  u"-" + value

        return value

    def type_second(self, value):