It looks as if that dial is showing (approximate) water temperatures using the Celsius scale.
The best rule is simply to keep the dial as low as possible for your needs. This will keep your bills down and help the planet. So, a bit of experimentation is called for. Try settting the dial to a fairly low setting and see if your water gets hot enough. To get you started, here's some guidelines as to temperatures:
Child care sites state that a baby's bath water should be between 32C and 37C. (So, even at the bottom of the dial you'll be getting water which might be a little too hot for a baby's bath).
The same sites state that, to prevent the risk of scalding, no house which has young children should ever have the thermostat set to above about 49C. (So, if you set the dial at 50C, you'll be heating water hot enough for it to pose a risk to a young child).
Other websites quote 50C to 60C as the range which can be described as 'hand hot'. (So, setting the dial to a maximum of 60C should give you water suitable for a bath as long as, of course, you can get a sufficient depth of water by only using water from the hot tank without adding any cold).
You should only need to set the thermostat above 60C if you want to take baths with a depth of water which can only be achieved by mixing water from both hot & cold taps. If so, you might try 75C.
The highest figure, 95C, is so close to boiling point (100C) that there can be no reason to set your thermostat this high. (That's hot enough to make coffee with!).
Use this figures to provide you with a starting point but, as I've said, you really ought to experiment to find the lowest setting appropriate for your household.
Hoping that this will help,
Chris