Hello

You can use one of maxim's real time clocks, the calculate sec,min,hour, day........

You can obtain an accuracy of 100% if you know how to use it well, also a nice feature is that you can use the built-in functions of I2C in PICBasic Pro to communicate with such RTCs.

I never have seen exact 1 sec displayed at exactly 1 sec duration, its some how 1 sec and 0.000034 some fractions...

So you better let the RTC calculate, and you control, its a nice idea, while you were thinking of a simple clock, you can do a full calender.