slant valve springs

for a valve spring compression tester,, you can use a sturdy drill press and a bathroom scale,,, force is force...

put the scale on the base of the drill press, insert the nose of the chuck into the spring and compress the spring to the installed height, read the scale...

be sure the spring is secure and horizontal,, if it would pop free it would give you a nasty hit. You would definately want safety guarding and a clamping fixture to check valve open pressures...