UKIDSS: 2.0 2.8 5.7
SDSS: 3

x2=0.8 x3=3.7

0 - v1
x2 - v2
x3 - v3


y = v1 + b*x + a*x^2

b*x2+a*x2^2 = v2-v1
b*x3+a*x3^2 = v3-v1

b*x2*x3+a*x2^2*x3 = (v2-v1)*x3
b*x2*x3+a*x2*x3^2 = (v3-v1)*x2

a = ((v2-v1)*x3-(v3-v1)*x2)/(x2*x3*(x2-x3))
b = (v2-v1-x2*((v2-v1)*x3-(v3-v1)*x2)/(x3*(x2-x3)))/x2

a=-((v2-v1)*3.7-(v3-v1)*0.8)/8.584
b= (v2-v1+0.8*((v2-v1)*3.7-(v3-v1)*0.8)/10.73)/0.8

y = -0.18243*v1+1.16379*v2+0.018639*v3