I have looked at various documentation and similar questions on here, but cannot seem to find the particular solution. Apologies if I have missed anything obvious or have re
You can give tooltipTemplate a function, and format the tooltip as you wish:
tooltipTemplate: function(v) {return someFunction(v.value);}
multiTooltipTemplate: function(v) {return someOtherFunction(v.value);}
Those given 'v' arguments contain lots of information besides the 'value' property. You can put a 'debugger' inside that function and inspect those yourself.