Measurements problem

[rfcomm2k]

I used the program to design stair I needed to replace going from ground level up to a porch. From the top of the footing to the BOTTOM of the top most tread is 50 1/8". Treads are 1" thick. The length from the face of the ledger board to the front face of the stringer is 77 1/16.

 

After the design was complete I laid out the treads and risers on a 2x12 and cut the first stringer. I set it into place and discovered it was short. I soon discovered this was because I made the tread cuts 10" instead of 11". I KNEW they were supposed to be 11", but I then decided to deduct 1" for the overhang of the tread, not paying attention to the fact that the treads themselves were 12".

 

So I again laid them out, this time being careful to mark the treads exactly 11" and risers exactly 6 5/16". I verified these dimensions in the software by using the tape measure tool.

 

It still looked short, so I did not cut it yet.

 

Referencing the attached file, the elevation detail, I measured using the tape measure tool from point A, which is the bottom front corner of the stringer, to point B, which is the top rear corner of the stringer. In the software, this measurement is 7' 7 7/8".

 

I then measured from the same two points on the actual stringer. I got 7' 4 1/2".

 

So then I did some geometry. A squared + B squared = C squared. The square root of 6 5/16* 6 5/16 +11*11 =.12.68257, almost 12 11/16. There are 7 treads. 7 * 12.68257 = 88.77801, just over 88 3/4. Which happens to be 7' 4 3/4", and is over 3" less than the same measurement made inside of the software.

 

A 3" discrepancy over less than 8 feet is significant.

 

Any comments?

 

porch steps.plan

[solver]

I can't follow what the problem is. 

 

I will say the tape measure tool is not the correct tool for the job. It's fine for quick, but not necessarily accurate measurements.

 

When needing accuracy, I create a CAD detail -- something you cannot do. You can use CAD lines carefully positioned and then one of the other measuring tools to get accurate measurements.

 

[rfcomm2k]

I think there should be a VERY big disclaimer when picking the tape measure tool that informs the user of this inaccuracy.

On a hunch, after reading your comment about the tape measure tool, I applied a point to point dimension to the elevation.

 

I got the same result, 7' 7 7/8".

 

Your drawing is not the measurement I was trying to confirm. Place the cross hairs on point A. Click and drag diagonally to point B, which is where the bottom rear corner of the tread meets the ledger board. THAT is the measurement that using the software shows 91 7/8", but simple geometry shows it is just over 88 3/4".

 

[solver]

The numbers work for me.

 

The triangle is the 4' 3", 6' 5", 92" sides.