Counting zeros gives varying values, how do I change this?

This is my code:

%% Import data

numfiles = 54; % number of excel files mydata=cell(numfiles,1); % defining size of mydata d=dir('Trial*.csv');

for i=7:length(mydata) % loop to import mutliple excel files

try
  mydata{i} = xlsread(d(i).name); % import files into mydata
catch
  disp([d(i).name 'read failed'])
end
  myfilename = sprintf('Trial%02d.csv', i); % define file name 
  mydata{i} = xlsread(myfilename); % import files into mydata

%% Perfrom Calculations

    %%Define variables 
      a= 9.81; % acceleration
      fps = 250; % frames per second

    %%Calculate Jump Height  
      no_of_zeros(i,1) = size(mydata{i,1},1) - nnz(mydata{i,1}(:,5)); %number of zeros
      no_of_frames = (no_of_zeros(i,1)/4); % number of frames 
      time = ((no_of_frames/fps)/2); % time up
      jumph(i,1)=((a*(time*time))/2); % jump height

Looking at the calculate jump height, it calculates correctly for the first 2 trials but then gives large over estimations for nealry all the other trails. It was a while ago I wrote this could someone clarify this line of code for me as this is where the trouble lies, I'm unsure with the ,1.

no_of_zeros(i,1) = size(mydata{i,1},1) - nnz(mydata{i,1}(:,5)); %number of zeros