Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_29703 ( "Model" text, "PPI (pixels per inch )" real, "ppcm (pixels per cm )" real, "Resolution" text, "Typical viewing distance (in/cm)" text, "Pixels per degree (PPD)" real )

### Question ###
How many different PPI does the model with ppcm of 87 have?

### Accurate SQL ###

SELECT COUNT("PPI (pixels per inch )") FROM table_29703 WHERE "ppcm (pixels per cm )" = '87'