A cheap way to determine contrast visually with a light table, and said negative under examination is a pair of cardboard cards with holes punched in them, and a stouffer step wedge. I suggest that a 120 sized 31 step one is nicest ($50 or so), but I started out using a 1/2" x 5" 21 step one that I got for free from a former graphics art printer who had tons of them idle after they went digital with prepress.
You flop the test neg and step wedge near one another on the light table or otherwise improvised light source plate. Put the card hole over the area of interst on the neg, and then slide the hole in the second card along the step wedge until the light tone matches. A human eye is very good at comparing and matching grey tones that are not to far apart. Make note of the value of the area. Then look at another area, compare to match its tone, and note it's area number. On a 31 step wedge the steps are .1 apart; on a 21 step .15 apart.
Say I have a neg of a landscape and am using a 31 step wedge to match tones. I look and see the thin area of the negative that I want to print as the first discernable shade away from total black, like the shadow under a bunch of cedar trees is matched by step, say 8. Then I look to the highlights other than the sky, say to a light toned rock that is not otherwise shaded, and comapre it- it is matched by the patch number 19.
Then I look to the sky, and find a light cloud that I want to show as light grey. It reads as a match to say 22. I would then find the usual contrast filter for a density spread from the specification sheet of the paper I am planning to use.
Lets say it's Ilford MGIV; oh where did that little piece of paper go after I openned the box/envelope? (mine is now taped to the wall beside the enlarger) Steps 19-8=11x.1 LogD per step=1.1, x100 for the ISO range of the paper needed , which I recall is about grade 2 or so. For over 20 years I never knew what the little tables Ilford put on that sheet had in them that could mean anything to me; now I do.
So I slap a grade 2 filter or whatever into the lamp house, or otherwise set my filters for grade 2, and then do a test print to figure how much time to make the rock be almost white. Once I find that time, I call that my base time.
For the clouds now figure the burn in time, added on top of the base time for just the sky area. In a .1 step step wedge, every three steps along is equal to a stop of light.
So in this example say the rock was just grey after 15 seconds of printing time in the test print (at whatever aperture). The are three steps (22-19=3) to the clouds that we want to see some light grey tone out of also above the value of the rock. Well rocks were light grey after 15 seconds; the sky then needs a 'stop' more time, ie another 15 seconds.
You can see how this leads to f/stop timing. Look up Ralph Lambrecht's approach to this; it is great once you strart to get your head around it.