Can some one tell me what the number in parentheses on the finder chart after the Mag value represents?
It looks something like this for CZ Ser:
Magn: 10.55 (1.06) V
Take a look at VSX for CZ Ser:
That notation comes from VSX note on Mag Range.
So my guess is CZ Ser varies over 1.06 magnitudes, centered on 10.55
Yes, in cases like this, when an amplitude is given (instead of a minimum magnitude), the maximum magnitude becomes a mean magnitude.
The mean magnitude of a pulsating variable, or any other variable with a sinusoidal-like light curve, will be more or les midway from maximum and minimum.
In the case of a detached eclipsing binary, the mean magnitude will be nearly the same as the maximum magnitude.
In the case of a dwarf nova, a flare stars or any other object undergoing outbursts, the mean magnitude will be closer to the quiescence state (minimum magnitude).
So when you see an amplitude in the minimum magnitude field, be prepared to open your mind and find things like these, when the maximum magnitude given is actually the minimum (!)
The key is understanding that, as soon as parentheses are seen, the maximum magnitude value is not longer working as such.
Having said that, nowadays we can adopt ranges for most stars, only that it is not a priority to do so, given the huge amount of data waiting to be imported or corrected. But if you find similar cases, you can submit revisions to VSX, e.g. deriving a range from ASAS-3 and ASAS-SN data.
I will do so for this star now, so in 10 minutes you will find a proper range given.