Calf strength screen?  Um, maybe not. Specifics matter.
Thanks to for putting this up. We would like to take this deeper, because it is very important.
This screen in our strong opinion is mostly for testing sub optimal endurance, sure there is some strength assessment going on but if you are trying to determine strength, is it single rep strength ? Very likely what he truly meant is how does the calf strength hold up at a 20 rep endurance challenge.  This is more accurate and we are fussing about specifics here, but specifics matter.
*However, the potentially BIG HOLE here in the assessment, is that “perceived” top end calf/heel raise ROM is not necessarily top end FULL ROM. If one side is truly weak, and you cannot get to top end strength (say the heel is 10% lower than the other side) someone has to be there to assess and notice that top end strength failure (a top end ROM that could reduce as endurance challenge continues, but someone has to be there to observe. Going on just “feel” alone is a bad recipe there). One like is not going to feel that top end range loss even if it is large, you will perceive the effort which could feel the same as the good side but actually be a loss.  And is 20 reps enough? Sure, it is a start but is your test really telling you what you think it is telling you ? This is being shown as a gross screen in our opinion but it has holes even as a screen.  Top end strength, something we talk about here often, is critical to performance. Top end loss means  terminal plantarflexion ROM is insufficient, and this can lead to a whole host of injuries and biomechanical flaws including achilles tendonopathy to mention just one. Remember, the gastroc does  not play alone here (and gastrocs crosses the knee joint posteriorly, some of the other posterior compartment muscles do not). There is soleus, peronei, tib posterior, long flexors etc. So are you doing your test with bent knee or locked ? It makes a difference if you are trying to tease things out.  Are you ramming your toes into flexion to get more out of them to make up for a loss elsewhere ? Is the forefoot or rearfoot inverting or everting  on the up or down phase ? These things matter. Specifics matter.  For example, you can see in this video that the hip is a little lateral to the foot placement. This will mean that the heel rise will result in a lateral forefoot weight bearing load. Do you want to see if the peronei are doing their job during the heel rise ? Well then you should go into a hip hike to posture the hip over the foot so that you can get the weight bearing transition to occur terminally over to the big toe, the peronei and lateral gastroc help drive that last little shift and if they are weak and you are not driving that last piece of the movement the test may not show you the whole picture you are thinking it is. Clue, if you cannot feel the lateral compartment contract to finalize that medial foot weight bearing load shift, you may be weak there. You better assess then.

Can you do 20 reps at 80% of the full plantarflexion ROM or can you do 20 reps at 100% full plantarflexion ROM ? There is a performance difference, and to the client unobserved, the 80% on one side may feel and perform like the 100% on the other side. But make no mistake, there is a world of difference.  Someone has to  watch that you are comparing apple to apples, and not apples to figs, oranges, turnips or squash.
-Dr.Shawn Allen, the gait guys