# What is 1.5%rdg + 4dgt for 15,23 V?

Where "Rdg"is for reading and "dgt"is for digits. So, 15,23 * 0,015 = 0,22845. Rounding to most significant digit it's 0,2. So is this correct? $$15,23 \pm 0,2$$

Since 4dgt is smaller we ignore it. Or am i doing this wrong? I need to find uncertainty in the way I did for a physics lab.

• What do "rdg" and "dgt" mean? I can guess, but I shouldn't have to. Are you using comma or point as a decimal mark? Commented Jun 3, 2020 at 17:59
• @ThePhoton "Rdg"is for reading and "dgt"is for digits. Commented Jun 3, 2020 at 18:08

$$\ 15.23 \times 0.015 = 0.23\$$ rounded to the same number of significant digits as the operand with the lowest number of significant digits (which is the 1.5%)
Then $$\\pm4\$$ digits on top of that means $$\\pm4\$$ of the least significant digit of your reading which was 15.23. The least significant digit of that reading is 0.01. You use the digit from the 15.23 and not the 1.5% because the digit error was quantified relative to your reading. It makes more sense if you just think about how your meter must have an finite minimum absolute error. If it was purely percentage error then it would imply the absolute error of your meter becomes infinitesimal as you approach a reading of zero.
Therefore $$\ \pm0.23 \pm0.04 = \pm0.27\$$