If you're looking for any function that return the value inside 0-100 it makes sense to check Sigmoid function. It produces values from 0 to 1, which are easily converted to 0 - 100;
This is my example on how to use Sigmoid approach.
Here is the normal Sigmoid function:
You have to choose the acceptance range start point starting from which you consider your accuracy value equal to
100%. Let it be
4. Zero value would be
-4. However your estimation is not
10 as you point out in your comment below. Thus you need to convert the coordinates where your
10 would become
4 for Sigmoid and
0 would become
-4. This is the simple linear expression. It would look like:
d(x) = 4/5 * x - 4, where
x - your estimation. Here is it on the chart.
Now what you only need is the absolute value of deviation from the estimated value. Say it would be diff and according to your comment below the actual work is measured as 200 units of whatever. Then you calculate:
Accuracy = Sigmoid(d(10 - |diff|)) * 100,
hence if your
diff = +/-5, your accuracy would be
50%, if your
diff = +/-190, your accuracy would be zero.
And here is the resulting graph for your case: