How Burmese year is calculated
The Burmese numerals are used in modern day Myanmar, also known as Burma. From 1837 to 1889 the Burmese year was determined according to the Chula Sakarat. During the mid-18th century the use of the calendar started to fall out of use due to the colonial influences, and the calendar was eventually replaced with the Georgian calendar after 1889.
More on Burmese dates
To translate the date for coins of 1889 and earlier, you add 639 to the date on the coin to get the Georgian equivalent. As the Burmese year starts in mid-April, it could also be correct to add 638 for coins that were minted prior to mid-April.
Reading the year
Here is the Burmese figure table: