A 36" measuring length will have an overall travel of 37.75 inches and an overall length of 42.375 inches. This would be the closest fit to 37 inches of required travel. By doing the math, I assume you have a mill with a 42 inch table. The recommended scale for a 42 inch table is a 32 inch scale. It has an overall length of 35.75 inches and a max travel of 31.125 inches. This scale will fit between the coolant return holes an the back of the mill table.
If you are attempting to push a 42 inch table to the bitter ends of its travel (37 inches) you will find that your accuracy at the ends of travel will drasticly fall off due to having all of the tables weight hanging off of one site of the saddle. It typically is not a good idea to expose the ways on the saddle while machining. It is better to machine what you can, then move your work over and finish. If your tolerances are super critical, you can mount a larger plate on top of the table then swing the head left to right. this prevents you from having to un-clamp your work.
Here is the link to the manuals on the acu-rite web site:
http://www.acu-rite.com/index.cfm?Pa...7200A0CC271CB6
AR-5 Scales are the oldest ones you will find.
MiniScales are next
Mate Scales were the only scale marketed with an analog output.
ENC150 scales are next and have the same footprint as MiniScales
SENC150 are the current design and also share the same footprint.
Another class of scales is the MicroScale and now the SENC50. These scales are much smaller in profile for applications that do not have a lot of room for a scale to mount.
For distances longer than 120 inches the AR10 and now the ENC250 uses a metal tape held in a series of sections and pulled under tension.
Probably too much information but I say it's always better to have the information you need before you need it.