Center controller reported descending an aircraft to an altitude below the minimum IFR altitude beca...

Narrative:

Aircraft X was inbound and requesting a visual approach. The pilot advised that he had the weather and requested a visual approach. I assigned him 3;000 feet and told him to report the field. Upon reaching 3;000 feet the pilot requested lower due to a thin layer/haze. I pulled up the MEA chart on the radar scope and misread that the minimum available altitude was 2;400 feet. I assigned him that altitude. Once the aircraft reached 2;800 feet; the MSAW alert flashed 2;600 feet. At that time; I attempted to stop the aircraft at 2;600 feet but he was unable to hear me on the radios. I attempted several times on various transmitters without success. The aircraft leveled at 2;400 feet and soon after reported the field in sight and requested to cancel his IFR. I could hear him but he couldn't hear me. I was able to relay through another aircraft on frequency.the altitudes on the radar scope are somewhat difficult to read as far as which areas have which MEA altitude minimums. There may not be a good fix but possibly moving the numbers to a more usable area of the map.

Original NASA ASRS Text

Title: Center Controller reported descending an aircraft to an altitude below the Minimum IFR Altitude because the numbers on the radar display were unclear.

Narrative: Aircraft X was inbound and requesting a visual approach. The pilot advised that he had the weather and requested a visual approach. I assigned him 3;000 feet and told him to report the field. Upon reaching 3;000 feet the pilot requested lower due to a thin layer/haze. I pulled up the MEA chart on the radar scope and misread that the minimum available altitude was 2;400 feet. I assigned him that altitude. Once the aircraft reached 2;800 feet; the MSAW alert flashed 2;600 feet. At that time; I attempted to stop the aircraft at 2;600 feet but he was unable to hear me on the radios. I attempted several times on various transmitters without success. The aircraft leveled at 2;400 feet and soon after reported the field in sight and requested to cancel his IFR. I could hear him but he couldn't hear me. I was able to relay through another aircraft on frequency.The altitudes on the radar scope are somewhat difficult to read as far as which areas have which MEA altitude minimums. There may not be a good fix but possibly moving the numbers to a more usable area of the map.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

Attributes
ACN	1530140
Time
Date	201804
Local Time Of Day	1201-1800
Place
Locale Reference	ZFW.ARTCC
State Reference	TX
Environment
Light	Daylight
Aircraft 1
Make Model Name	EMB-505 / Phenom 300
Operating Under FAR Part	Part 135
Flight Phase	Initial Approach
Route In Use	Visual Approach
Flight Plan	IFR
Person 1
Function	Enroute
Qualification	Air Traffic Control Fully Certified
Experience	Air Traffic Control Time Certified In Pos 1 (yrs) 7.0
Events
Anomaly	ATC Issue All Types Deviation - Procedural Published Material / Policy Inflight Event / Encounter CFTT / CFIT

Center controller reported descending an aircraft to an altitude below the minimum IFR altitude because the numbers on the radar display were unclear.