Answer:
Explanation:
When you record measurements in the lab, you can estimate one more signficant digit than the smallest mark on the instrument.
For instance, if you use a graduated cylinder whose marks at are 1 mililiter, you can estimate 0.5 mililiters.
But when you use digital instruments, such as a digital top loading balance, you cannot estimate an additional digit; so you must write down the same readout.
Regarding the number of significant digits, take into account that the last digit of the readout is uncertain. The real measure can be in the interval (3.0695 - 3.0705).
In other words, the measure can be read as 3.070 g ± 0.0005 g.
From that, the last digit in the measure, the last 0 in 3.070, is uncertain.
Remember that the significant figures of a measure include the first uncertain digit. So, all the digits in 3.070 g are signficant, and you must record all the four digits: 3.070.