Open the Options and select Meters for the Range Units under the Units tab. That’s because while we want to keep drawing in Millimeters in the model space, it makes much more sense to enter and read Range values using the Meter unit.

Now go to the Digits tab and select 0.00 from the Range Digits combo box; that way AutoRebar will display the second significant digit for the range, i.e. it will round to the Centimeter.

Click the Mark command and select the Rebar (you may also pre-select the Rebar and run the Mark command afterwards).

Pick any two points to place the Mark. From now on this two objects will be linked together and data will be transferred from one to the other so that changes can be tracked in real-time (try to stretch the Rebar and see what happens to the Mark).

Double click the Mark to edit the grouping data. We want this Mark to define a group of single bars, placed 200mm apart along a 10m wide range:

S = 200mm (bar spacing)

E = 10m (range along which the bars are placed)
That sums up to (10m / 200mm) + 1 = 50 + 1 = 51 bars.

Click Ok or press Enter to close the Edit form and verify that the Marks does show N = 51 as the total numer of bars in the range.

Start the BBS command and pick a point to place the Bar Bending Schedule.

Double click the Mark again to edit the grouping data. This time we want the Mark to refer to a boundle of 2 double bars (for instance a double bar at the near face and a double bar at the far face) for a total of 4 bars placed, as before, 200mm apart along a 10m wide range:

n = 2 (double bars)

a = 1, b = 1 (will show up as (1+1))

S = 200mm (bar spacing)

E = 10m (range along which the bundle of 2∙(1+1) bars are placed)
That will sum up to 4 ∙ [(10m / 200mm) + 1] = 204 bars.

Click Ok or press enter to close the Edit form and run the BBS command again to update the Schedule. The total amount of steel is now 4 times as much.

The general formula used by AutoRebar to calculate the number of bars specified by a single Mark is as follows:
N = [n ∙ (a + b)] ∙ [floor(E / s) + 1]
where floor(x) is the largest integer less than or equal to x.