When physicists say "estimate" in this context, they mean "take into account this fourth-order tiny effect by using an approximate theory of said effect with accuracy of a few percent, and then use 1.2 meters when it's really 1.0 so you overestimate by 10%".
It's like when you take a caliper and measure the width of an object, you typically neglect the error due to thermal expansion of the caliper since it's hotter/colder than when it was marked with gradations. If you're really anal about uncertainty (like these guys), you'd estimate the effect of this expansion and say "a conservative estimate says this contributes an uncertainty of 0.0003 mm".
It's like when you take a caliper and measure the width of an object, you typically neglect the error due to thermal expansion of the caliper since it's hotter/colder than when it was marked with gradations. If you're really anal about uncertainty (like these guys), you'd estimate the effect of this expansion and say "a conservative estimate says this contributes an uncertainty of 0.0003 mm".