I don't know the meaning of the phrase "accurate to within" in a sentence like "It is accurate to within 0.07mm". I need some assistance.
It means that the accuracy is measurable within a range of that size.
For example, if a GPS device was said be "accurate within 30cm", that would mean that any position it gives could actually be up to 30cm out in any direction. It doesn't mean that it will always be out, or that it will always be 30cm - it means that is the maximum, or the limit of the range that it will be out.
As another example - a cheap watch might be said to be accurate to "within less than a second per day" - that means that it could either lose or gain a fraction of a second each day, which could add up over time to be a considerable innacuracy. More expensive watches may boast greater accuracy.
0.07mm is a very small measurement - depending on what the application is (you didn't say in your question) that could be considered either extremely accurate, or in the case where precision is very important, it could be an unacceptable degree of inaccuracy.
"accurate to within" defines what is actually represented as +/- error in the calculation of a metric. So according to your statement, the acceptable range is (+/- 0.07mm).
For e.g., If your vernier caliper measures the length of some object as 44.30mm, then the acceptable lengths would be between 44.23mm and 44.37mm.