In article ,
DaddyMonkey wrote:
If deflection is the vertical movement of the floor joist span measured
at midpoint, there needs to be a set (known) weight to obtain this
measurement.

A small child standing on the center of the joist will give a different
reading than an elephant.


Most building codes have the following limits for residental construction.
Total deflection 1/240 (for both dead and live load)
Live load deflection 1/360

The dead load is the mass of the floor and fixed structure.
The live load is what can come and go such as people, furniture, etc.

A typical building code is 40 lbs/sq ft under live load for residental
construction. For some other types of construction the live load requirement
can increase quite a bit. For example a library under current codes has a
maximum deflection of 1/360 with a live load of 150 lbs/sq ft..