Assuming the columns appear in time order, the first row (for example) indicates that total construction through each period went
0, 0+45 = 45, 45+135 = 180, 180+405 = 585, 585+1010 = 1595, ..., 2230+0 = 2230.
Construction was halfway through at 2230/2 = 1115. This occurred during period 4, because at the end of period 3 the total was 585, at the end of period 4 the total was 1595, and 585 <= 1115 < 1595.
This appears to be the result reported by the [Median] column, which gives the index of the period (starting at 1 on the left).
You can code this in your favorite language. The table is so small (100 rows), though, that a spreadsheet will be convenient, if only for checking what you do more formally in Python or whatever. Here's what it might look like:
The first three data rows have the same values as yours. The next two data rows (surrounded by blank lines) are chosen further down in your table. The last five data rows exercise the algorithm a bit.
(Note, as shown in the last two lines of the spreadsheet, how Excel chooses the later period whenever the middle falls exactly between two periods. This isn't necessarily the "right" answer, but it's a valid one.)
Here are the formulas in columns H:R:
You don't have to type them all. The only typing needed is:
=H2+A2 in I2. Drag this through O2. This computes the cumulative sums. It requires that columns A:G are in chronological order.
=O2/2 in P2. This finds half the total.
=Match(P2,H2:O2,1) in Q2. This indexes the column where construction was half complete.
=Offset($A$1:$G$1,0 0, Q2-1, 1, 1) in R2. This obtains the column heading corresponding to the index.
Then paste 0 in all of column H and drag I2:R2 down to as many rows as needed.
This effectively serves as pseudocode for the algorithm. The trickiest part will be the search to implement Excel's MATCH function. But that doesn't require any craft: it's not inefficient to search each array of cumulative sums sequentially (rather than with the preferred binary search algorithm) because these arrays are so short.
Best Answer
A couple of ways to accomplish these types of tasks.
1. Round ([myfield], 2) This works for field calculator, labeling, etc.
2. in the layer dialog left click the label column and select format labels
3. select the number format in the field properties and change the number of decimals.