Measuring slant lathe bed

[Pavel Capek]

Hello I recently buy new to me lathe. The lathe needs certain level of reconditioning. But I stopped on initial meassuring. I cannot figure it out how to check if top saddle ways (for cross slide) are falling down or rising up.
The lathe has a slanted bed, but top of a crosslide is in the level. I hope it will be more clear from side view of cross slide I attached. I also highlight with red line profile of the bed.

Please, Can someone point me up how to properly measure the saddle ways for cross slide? I will be more than greatfull for your comments.

Thank you for your patient with me. Have a nice day, Pavel