First draw a normal number .
draw a 1 cm line above 3 and name the point B and join it to 0.
take a compass and measure this line segment and draw an arc from 0 cutting the number line.
this point is root 10.
hypotenuse square =sum of the squares of other two sides
=square of 3+ square of 1= 9+1=10
hypotenuse= root 10
lol at least tell him the basics of the spiral method
notify him about the units
An easier way , draw a line l , make a point 0 on it ,
now from 0 as center and radius 3 cm draw an arc on line l ,
name the intersecting point as A
now from A draw a perpendicular of 1cm
name the point where it ends as B
now join 0B
take 0B as radius and draw an arc on line l
name it as point C
point C is root10
by Pythagoras theorem
1^2 + 3^2 as the 90 degree angle and the base respectively
therefore root 10 = root over 3^2 + 1^2  being root over 9 + 1
and there you have it