# The turf GvX: growth versus expected

We’ve been working on this one for a long time. We’ve had the turfgrass speedometer (or speedo), which can also be called the growth ratio. Both of those names have some problems. Not distinct enough, in the case of the growth ratio, and too distinct, perhaps, in the case of the speedo.

I’m pleased to introduce a new name for the same metric: Turf GvX. This rolls off the tongue, makes a nice #TurfGvX hashtag, and it is a short form of turfgrass **growth** *versus* **expected** [growth].

I have this recommendation for the standard value for the GvX.

- Take the 14 day average of clipping volume, expressed in units of mL/m
^{2}/day. - Take the 14 day average of growth potential (GP), expressed on the 0 to 1 scale, and shift this backwards one day relative to the clipping volume average. That is, the clipping volume is the average of today and the preceding 13 days. The GP average is the average of yesterday and the preceding 13 days. The reason for this shift is to be able to generate a GvX value immediately once a day’s clipping volume data are available.
- The GvX expressed in the standard way will be:

$$ \text{GvX} = \frac{ClipVol_{14}}{20 \times GP_{14}} \times 100 $$

where $ClipVol_{14}$ is the 14 day average of clipping volume and $GP_{14}$ is the 14 day growth potential average.

This is taking the growth and comparing it to the expected growth. Thus, GvX.