That's why it's a place holder...
0's at the end of a number, without decimal places, are not significant.
0's after the decimal, before numbers, are not significant if 0 precedes the decimal.
Otherwise, you could call 2 ppm .000002 and say it's 6 sig dig, when it is only 1!
Consider scientific notation- a.bc x 10 to n power- a.bc is sig, not the location of the decimal point, with regards to accuracy/precision of measurement
When you mult/div numbers, the lowest number of sig dig in any of the factors is the number of sig dig in the product
When you add/sub, the number with the highest multiple of 10 becomes you last sig dig (1,250 + 2, is still 1250 for significance...)