There are couple of errors in that. First, water does not weigh exactly a gram at 20 °C. It weighs 0.998203. In the video he weighs out 50 mL of solution and finds it weighs 50 grams. He then calculates the SG as 50/52 = 1.040. The correct conclusion from this measurement is SG = 52/(50*0.998203) = 1.042. That's not a lot of change but significantly closer to the hydrometer reading of 1.05.
Second, the formula he gives, -36.158S*S + 1183.75*S - 147.47 yields the strength of the solution w/w. That's not very useful. w/v is much more useful as you simply divide the grams of CaCl2.0H2O you need by the w/v and measure out that many ml. The w/v formula is
g/L = -684.57 + 175.12*SG + 509.45*SG*SG
Of course if you have a scale and no graduated cylinder you will have to use the w/w method. w/v is easily obtained from the g/L. You figure out how many mL you need from the g/L formula and then multiply that by 0.998203*SG to get the weight of that many mL.
